What the concrete calculators cover
A concrete job is a set of separate quantities: the volume of each shape, the unit that volume is bought in, the mix, the forms that hold it, the reinforcement and the cure. This page lists the calculators in that order and says what each answer rests on, so a figure can be checked rather than trusted. The groups are the order, the shapes, the mix, placing and curing, the formwork, the reinforcement, screeds and the weight conversions, and a last group of pages that test a number against a published method.
The shapes group counts what a drawing hides: the edge bands and beams of a raft, the bell at the foot of a drilled pier, the steps of a footing on a sloping site, the volume a post takes out of its own hole. The order group turns a volume into bags, cubic yards or cubic metres and back again, so a bagged job can be set against a delivery. Where the answer is a weight, the conversion pairs give fresh concrete, rubble and screed in both directions.
How the answers are worked out
Volumes are length by width by depth, and the concrete calculator prints the result twice: the net volume, and the volume with the waste factor the reader sets. That keeps the allowance visible, so the part of an order that is shape and the part that is margin are never mixed. Bag counts use the published yield of each bag size the bag calculator lists, which include the bag sizes stocked in metric markets, and the count is rounded up to whole bags. Compare the yield on your own bag with the one the calculator uses.
The mix calculators follow ACI 211.1. The mix design calculator works by absolute volume and takes its water, air and coarse aggregate figures from that standard's own tables, which the site does not reproduce. Strength against water-cement ratio follows Abrams' relation, with constants that depend on the materials, the age and the curing, and the page says plainly that no calculation establishes a strength: only specimens tested under ASTM C39 or EN 12390 do. A delivered batch is checked with the relative yield of ASTM C138, and aggregate moisture has its own page because a mix design assumes aggregate in the saturated surface-dry condition.
Placing and curing rest on named methods as well. The evaporation calculator uses the ACI 305R equation with the widely cited threshold for plastic shrinkage risk, the maturity calculator is the Nurse-Saul function of ASTM C1074, and the formwork calculators take ACI 347R, which is why the rate of placement, and not only the height, is an input to the pressure on a form.
Units and documents by market
The market setting chooses the system the answers appear in: inch-pound units for the United States, metric for the United Kingdom, Australia and Canada. Every calculator restates its answer in the other system, so a supplier's ticket can be read in the units it was written in. The concrete code the site names for each market is ACI 318-19 for the United States, BS EN 1992 (Eurocode 2) for the United Kingdom, AS 3600 for Australia and CSA A23.3 for Canada. The table shows where the calculators on this page cite a document from each market.
| Market | Ordered by | Measured as | Worth knowing |
|---|---|---|---|
| United States | Cubic yards and bags, with the conversions between them | ACI 211.1 for the mix, ACI 305R for evaporation, ACI 347R for form pressure, ACI 318 for laps, hooks and development length | ASTM test methods carry the yield, unit weight, air content and strength checks. |
| United Kingdom | Cubic metres, with answers restated in the other system | BS 8204-1 for screed thickness, reported through the Mineral Products Association data sheet; BS 4483 for the standard fabric | The development length and one-way slab pages say they apply ACI 318, and name Eurocode 2 as working differently. |
| Australia | Cubic metres, with answers restated in the other system | AS 3600 is named by the one-way slab thickness page, which applies ACI 318 and says AS 3600 controls deflection through its own provisions | Few pages here apply an Australian document: read their results against the code your state adopts, which the site names as the NCC. |
| Canada | Cubic metres, metric first, with answers restated in the other system | CSA A23.3 is named by the development length and one-way slab pages, which apply ACI 318 and say their answer is not a CSA figure | Provincial and municipal amendments govern over any model code, as the site's own market note says. |
Allowance, rounding and the last bag
Counts are rounded up because a bag, a bar or a sheet of mesh is bought whole. The rebar calculator counts sticks from stock lengths and adds a lap allowance; the chair calculator counts supports from a spacing the reader enters, because the right spacing depends on the bar size, the stiffness of the mat and whether the mat is walked on. Where a figure belongs to a product, such as the coverage of a curing compound or the yield of a mix, it is an input and not a built-in table, so the data sheet in your hand decides it.
The order the questions come in
The groups follow the order a pour asks its questions in. The shape gives the volume; the order group turns it into a purchase; the mix group says what is in it and what strength to expect; the placing group deals with vibration, pumping, temperature, joints and cure; the formwork group gives the pressure the forms must resist; and the reinforcement group counts bar, mesh, chairs and the length of a lap or a hook. A figure in one group feeds the next: the volume sets the bags, the rate of placement sets the form pressure, and the weather sets the cure.
What the calculators leave to others
Reinforcement is a design decision, and the rebar calculators count what a drawing specifies; they do not choose the bar. The checks group tests a number against a published method, such as a beam's nominal moment capacity or a column's axial capacity, and the designer's detail decides the member. Control joint spacing is a rule of thumb and the page states it as one, and the screed pages follow the thickness rules of the standards and data sheets they cite. A figure from any page here is a planning quantity: the supplier's ticket and the engineer's drawing govern.
Which calculator for which job
Every concrete calculator on the site, grouped by what it does for the material, with the reason it is here. Open the one that matches the question in front of you; each restates its answer in both unit systems.
Work out how much to order
A size in, a volume and a bag count out, and the conversions between them for comparing a bagged job with a delivery.
| Calculator | What it does for concrete |
|---|---|
| Concrete Calculator | The ordering figure for a slab: volume in the unit you buy, the bag count and the allowance, in one result. |
| Concrete Driveway Calculator | A driveway's concrete and the gravel base beneath it, from its length, width and thickness. |
| Concrete Bag Calculator | How many premixed bags a small pour or a run of fence-post footings takes. |
| Concrete Bags to Cubic Yards Calculator | Turns a bag count into a volume so a bagged job can be set against a delivery. |
| Cubic Yards to Concrete Bags Calculator | Turns a volume into bags, for the pour too small for a truck to be worth sending. |
| Reverse Concrete Slab Solver | Starts from the bags you already hold and gives the slab area they will cover. |
| Concrete Relative Yield Calculator (ASTM C138) | Checks that a delivered batch produced the volume it was designed to, from a weighed test. |
Volumes for the shape you are pouring
Footings, piers, steps, walls, curbs and slabs each hide a volume the plan does not show; these count it.
| Calculator | What it does for concrete |
|---|---|
| Circular Pier / Cylinder Concrete Calculator | Concrete in round piers, columns or bollards from their diameter and depth. |
| Drilled Pier Concrete Volume Calculator (Straight Shaft / Belled) | A drilled shaft's volume, with the optional bell at its base counted. |
| Continuous Footing / Grade Beam Volume Calculator | A strip footing or grade beam from its length, width and depth. |
| Raft Slab Concrete Volume Calculator (Edge Thickenings and Downstands) | A raft slab plus the edge bands and beams that the plan does not draw as concrete. |
| Stepped Foundation Calculator (Steps, Bays and Overlaps on a Slope) | How a sloping site steps a foundation, so each step's concrete is counted. |
| Retaining Wall Footing Sizing Calculator | A retaining wall's footing from a rule-of-thumb width, then its concrete. |
| Poured Retaining Wall Stem Concrete Volume Calculator | The stem above the footing, including a batter on its face. |
| Structural Column Pour Calculator | One or more square or rectangular columns, poured in a single lift. |
| Concrete Steps Volume Calculator (Solid and Waist-Slab Flights) | A flight of steps, solid on the ground or cast on a sloping waist slab. |
| Built-In Bench/Planter Seat Wall Concrete Volume Calculator | A built-in bench or planter wall, the concrete behind a garden seat. |
| Concrete Curb and Gutter Volume Calculator | A combined curb and gutter section, counted along a run. |
| Deck Footing Calculator | How many footings a deck's perimeter wants at the usual spacing, before each is poured. |
| Post Hole Concrete Calculator | Fence and post holes, allowing for the volume the post itself takes up. |
| Traffic Sign Post Foundation Concrete Calculator | A cylindrical foundation for a traffic sign post. |
| Sump Pit & Catch Basin Concrete Calculator | An open-top sump pit or catch basin, with its hollow taken out. |
| Concrete Barrier (Jersey Barrier) Segment Count Calculator | How many precast barrier segments a run of temporary or permanent barrier needs. |
| Tremie Pipe Safe Withdrawal & Embedment Calculator | How far a tremie pipe can be raised during an underwater or drilled-shaft pour. |
| Insulated Concrete Form (ICF) Block Count Calculator | Insulating concrete form blocks for a foundation or wall, where the forms stay as permanent formwork. |
| Concrete Pavement Dowel Bar Calculator | The dowel bars at a concrete pavement joint, counted from published industry guidance. |
| Concrete Sidewalk Control Joint Spacing Calculator | How many control joints a sidewalk run needs. |
Mix design, strength and test results
What is in the mix, what strength the water-cement ratio gives, and how a trial batch or a test cylinder corrects the paper.
| Calculator | What it does for concrete |
|---|---|
| Concrete Mix Design Calculator — ACI 211.1 Absolute Volume Method | The fine aggregate in a mix by absolute volume, from the cement, water and stone chosen. |
| Concrete Mix Ratio Calculator | Breaks a cement, sand and gravel ratio into volumes and bags for hand-mixed work. |
| ACI 211.1 Water-Cement Ratio Calculator | The water a mix needs to reach a target water-cement ratio. |
| Water-Cement Ratio and Concrete Strength Calculator (Abrams' Law) | The strength a water-cement ratio is likely to give, and the ratio a target strength needs. |
| Aggregate Fineness Modulus Calculator (ASTM C136) | A sand or stone's fineness modulus from a sieve analysis. |
| Concrete Aggregate Moisture Correction Calculator | Corrects batch weights and water for the moisture already in the sand and stone. |
| Concrete Air-Entrainment Admixture Dosage Calculator | The admixture volume a batch needs from its dosage rate. |
| Fly Ash / Silica Fume SCM Replacement Calculator | Splits the cementitious content between portland cement and fly ash or silica fume. |
| Concrete Trial Batch Yield Adjustment Calculator | Corrects a mix's quantities when a trial batch's measured yield differs from the design. |
| Concrete Slump Flow Test Calculator (ASTM C1611) | Classifies a self-consolidating mix's flow and viscosity from slump-flow readings. |
| Fiber-Reinforced Concrete (FRC) Dosage Calculator | The mass of synthetic micro-fibre a fibre-reinforced pour takes. |
| Concrete Unit Weight (Density) Calculator (ASTM C138) | The fresh unit weight of a mix from a measured test. |
| Concrete Elastic Modulus Calculator (ACI 318) | A mix's modulus of elasticity from its unit weight and compressive strength. |
| Concrete MPa to PSI Calculator | Turns a metric strength grade into pounds per square inch for a US specification. |
| Concrete PSI to MPa Calculator | Turns pounds per square inch into megapascals for a metric specification. |
| Embodied Carbon in Concrete Calculator | A concrete element's cradle-to-gate carbon, and what replacing cement with slag or fly ash changes. |
Placing, finishing and curing
Getting it in, consolidated, jointed and kept wet or warm for as long as it needs.
| Calculator | What it does for concrete |
|---|---|
| Concrete Poker Vibrator Insertion Spacing Calculator | Poker insertion spacing, so each vibrator radius overlaps the last. |
| Concrete Pump Line Friction Loss Calculator | The equivalent pumping distance and pressure loss in a pump line. |
| Concrete Evaporation Rate Calculator | The surface evaporation rate, to judge plastic shrinkage risk before the pour. |
| Concrete Mix Temperature and Ice Substitution Calculator | Mix temperature from its ingredients, and the ice or hot water that corrects it. |
| Concrete Maturity Method Calculator (Nurse-Saul) | A pour's maturity index from its temperature history and elapsed time. |
| Mass Concrete Thermal Gradient Calculator | The core-to-surface temperature difference of a mass pour, set against the cracking limit. |
| Concrete Curing Blanket Calculator | Insulated blankets to protect a cold-weather pour. |
| Concrete Curing Compound Coverage Calculator | The liquid curing compound a slab surface takes. |
| Concrete Control Joint Spacing Calculator | The recommended spacing of control joints to keep a slab's cracks where they were planned. |
| Concrete Expansion Joint Filler Calculator | The sealant or filler an expansion joint takes. |
| Concrete Resurfacer and Patch Calculator | Bags of resurfacer or patching mortar for a worn slab. |
| Concrete Washout Basin Solidifier Dosage Calculator | The solidifying agent for a washout basin's liquid waste. |
Formwork and bracing
The boards that contain a slab and the pressure that wall and column forms must resist.
| Calculator | What it does for concrete |
|---|---|
| Concrete Formwork Calculator | The edge-form boards and surface area that contain a slab. |
| Wall Formwork and Shuttering Calculator (Form Area, Ties, Wales and Studs for a Poured Wall) | Both faces of a poured wall's form, with its stop-ends, box-outs, tie grid, wales and studs. |
| ACI 347 Wall Formwork Rate-of-Placement Pressure Calculator | The maximum lateral pressure ordinary concrete puts on wall forms. |
| ACI 347 Column Formwork Pressure Calculator | The same pressure on column forms, which fill faster. |
| SCC Formwork Lateral Pressure Calculator | The full hydrostatic pressure when the concrete is self-consolidating. |
| Concrete Formwork Tie Spacing Calculator | The widest square-grid tie spacing a given pressure and tie capacity allow. |
| Formwork Brace & Kicker Force Calculator | The axial load in a wall-form brace, from the pressure on its strip. |
Reinforcement
Bar and mesh quantities, the laps, hooks and chairs that make the layout buildable, and the post-tensioning and masonry reinforcement pages that count steel in or beside the concrete.
| Calculator | What it does for concrete |
|---|---|
| Rebar Calculator | The bar length and the number of sticks a rectangular slab needs at a given spacing. |
| Rebar Weight Calculator | The weight of a bar order, for delivery and handling. |
| Rebar Chair and Bolster Count Calculator | The chairs, bolsters and spacers that keep a mat's cover under foot traffic. |
| Rebar Lap Splice Length Calculator (ACI 318) | A lap splice worked from the development length and the bars being spliced. |
| Rebar Standard Hook Development and Cut-Length Calculator | The embedment a standard hook develops and the bar its bend uses. |
| Rebar Development Length Calculator (ACI 318) | The tension development length of a bar by the simplified method. |
| Welded Wire Mesh Calculator — Reinforcing Mesh Sheets for a Slab | The sheets of welded wire mesh a slab takes at your sheet size and lap. |
| Concrete Slab + Rebar Combined Mass Calculator | The mass of a reinforced slab, concrete and bar together. |
| Post-Tensioned Anchor Seating Loss Calculator | The prestress a short post-tensioned tendon loses to the draw-in of its anchor wedges. |
| Masonry Bond Beam Rebar Calculator | The length and mass of bar in the horizontal bond beam courses of a reinforced block wall. |
| Seismic Masonry Horizontal Reinforcement Ratio Calculator | A reinforced masonry wall's horizontal steel ratio, set against a common minimum for seismic work. |
Screeds laid over a slab
A thin sand-and-cement or liquid topping is concrete's close relative, ordered in its own terms and laid to its own thickness rules.
| Calculator | What it does for concrete |
|---|---|
| Floor Screed Calculator — Sand and Cement, Bagged or Liquid | A floor's screed by depth, as sand and cement, bagged premix or liquid. |
| Floor Screed Thickness Calculator — Bonded, Unbonded and Floating | How thick a bonded, unbonded or floating screed must be for its duty. |
| Heated Screed Volume Calculator | The screed an underfloor heating build-up takes over the pipe crown. |
Weights and rubble conversions
Fresh concrete, demolished concrete and screed as weight and as volume, for haulage and disposal.
| Calculator | What it does for concrete |
|---|---|
| Wet Concrete Cubic Yards to Tons Calculator | Fresh concrete as weight, for haulage and for a weight-based delivery. |
| Wet Concrete Tons to Cubic Yards Calculator | A fresh concrete tonnage back into volume. |
| Concrete Rubble Cubic Yards to Tons Calculator | Demolished concrete as weight, for loads and disposal limits. |
| Concrete Rubble Tons to Cubic Yards Calculator | A rubble tonnage back into volume, to check capacity. |
| Floor Screed Cubic Yards to Tons Calculator | Screed volume as weight, for ordering and haulage. |
| Floor Screed Tons to Cubic Yards Calculator | A screed tonnage back into volume. |
Checks against a code figure
Pages that test a number against a published method. They check a figure; they do not design the member.
| Calculator | What it does for concrete |
|---|---|
| Reinforced Concrete Beam Moment Capacity Calculator (ACI 318) | A singly reinforced beam's nominal moment capacity, as a figure to compare with the design. |
| Reinforced Concrete Tied Column Axial Capacity Calculator (ACI 318) | A tied column's nominal axial capacity, as a figure to compare with the design. |
| One-Way Slab Minimum Thickness Calculator (ACI 318) | The minimum slab thickness the code lets you skip a deflection check at, for a span and support. |
| Concrete Anchor Bolt Breakout Capacity Calculator (ACI 318) | A single anchor's basic concrete breakout capacity by the published method. |
| Post-Installed Concrete Anchor Drill Depth Calculator | The depth to drill for a required embedment, and whether your anchor reaches it. |
Whole jobs, taken off
A job takeoff asks for the dimensions once and returns every line the job needs, each from its own calculator. These are the ones where concrete is a main line.
- Concrete slab
A slab taken off whole: the concrete, the reinforcement and the edge forms from one set of dimensions.
- Strip footing
A continuous footing under a wall: its concrete, the backfill and the reinforcement.
- Concrete driveway
A driveway slab with its sub-base, mesh and joint spacing, and the dig, forms and cure around it.
Read an answer backwards
When you start from what you hold and want to know what it will cover, these pages run the same calculators in reverse.
Worked examples
A job worked through with its inputs and its working shown, so you can see the figures before you enter your own.
- Garden room slab
A small slab worked from the dig to the cure, with the concrete, mesh and forms in the order they are bought.
- Concrete driveway replaced
A drive broken out and re-laid: what the old slab leaves behind and what the new one asks for.
- A garden shed base, in cubic metres
Concrete for a garden shed base 3.6 by 2.4 m, 10 cm deep
- A rectangular slab, in cubic yards
Concrete for a 20 by 30 ft slab, 4 in thick
- A garage base, in sheets of steel mesh
Welded steel mesh for a 6 by 4 m single garage base
- A garage slab's grid, in stock lengths of bar
Rebar for a 24 by 24 ft garage slab on a square grid
Reference tables
- Production rates by operation
How long each operation takes one person, in person-hours per unit of work.
- Bulk densities of construction materials
What a cubic metre of loose material actually weighs, in both systems, as this site's calculators compute it.
Guides
The practice behind the numbers: how the work is done, what goes wrong and how to check it.
- The Master Guide to Pouring a Professional Concrete Slab
A pour told in order, from subgrade compaction the week before to the joints, the cure, and the cracks that appear a month later.
- Pouring a Slab From Bagged Mix
A pallet on the drive, no truck access, and a fixed bag count: the area those bags really cover, and the barrow runs and mixing hours behind it.
- Footings, Piers and Frost Depth
Every footing answers to two independent depths — competent bearing and the frost line — and the deeper of the two governs the dig.
- Designing a Concrete Mix and Reading the Submittal
A mix submittal makes three claims - water-cement ratio, sand grading and stiffness - and the review is proving they agree with each other.
- Placing and Pumping Concrete
A field guide to moving ready-mixed concrete from truck to formwork with its water-cement ratio, air content and workability still intact.
- Curing Concrete in Heat and Cold
Curing is a race between hydration and evaporation, and every measure on a concrete pour either slows one clock or speeds the other.
- Jointing Concrete Flatwork
Flatwork concrete cracks whether you plan for it or not, so jointing is the trade of choosing the crack line before the slab does.
- Building and Bracing Formwork
Formwork pressure follows the rate you fill at, so the pour plan sizes the ties, walers and bracing long before a panel is cut.
- Bracing Formwork for the Pressure a Pour Actually Makes
A raker resists what would tip a wall form over, not the concrete's push on the sheathing — until the form loses its opposite face and the two become one load.
- Detailing Rebar: Laps, Hooks and Cover
A concrete field guide to what actually develops a reinforcing bar on site — bond length, hooks, cover and the details that quietly shorten all three.
- Rebar Hooks: The Length That Is Not on the Drawing
A hook is a symbol on the section and a real length of steel in the yard. What the bend and its tail consume, and why bar lists come up short.
- Ordering Concrete for a Column Pour
A column lift is under ten cubic metres and has no tolerance either way: short leaves an unplanned joint, long leaves concrete you have to dispose of.
- Specifying Lower-Carbon Concrete
Cement replacement, leaner sections, or a different frame material - three levers on a concrete frame, and only two are still open the month before a pour.
- Stepping Foundations Down a Sloping Site
A metre of fall turns one strip footing into a staircase of separate pours. Where the step height, the lap and the made-up ground come from.
- A Seat Wall: Height, Depth and the Concrete Under It
Sitting height is a sum with the cap inside it, seat depth is bought in cubic metres, and the footing is sized by frost because nothing above it weighs enough.
- Anchoring Into Concrete and Masonry
Every concrete anchor drags a cone of substrate with it — edge distance, spacing and embedment are all arguments about that cone.
Terms
How the numbers are worked out
Every calculator names the method it uses and the standard or guidance behind it. These are the methods the most of the calculators above rest on, and the published documents they cite.
Methods
- Concrete Mix Design and Fresh-Concrete Behaviour
Why a litre of water added on site costs strength permanently, why yield is the sum of absolute volumes rather than of loose ones, and why strength is a function of temperature and time together rather than of age. Applies to 17 of the calculators above.
- Volume from Geometry, and the Order That Follows
Why the depth carries almost all the risk in a volume, why an excavation holds far more than its plan area suggests, and why a bag's yield is not its weight divided by a density. Applies to 13 of the calculators above.
- Quantity, Waste and Rounding
Why a material count is a ceiling function rather than a division, and why the waste factor — not the geometry — carries the risk. Applies to 11 of the calculators above.
- Unit Conversion, Exactness and Rounding
Why most conversion factors carry no uncertainty at all, which ones hide a material assumption, and why converting a measurement can never make it more precise than it was. Applies to 10 of the calculators above.
- Formwork Pressure
Why a column form sees full hydrostatic pressure and a wall form usually does not, and why temperature belongs in the equation. Applies to 5 of the calculators above.
- Mass from Volume and Density
Why a rolled steel section's mass is read from a table rather than computed, why one material has five densities, and why a tonne of wet sand is less sand. Applies to 5 of the calculators above.
Standards cited
- ACI 318
Cited by 10 of the calculators above.
- ACI 211.1
Cited by 4 of the calculators above.
- ACI 347R
Cited by 4 of the calculators above.
- ASTM A615
Cited by 3 of the calculators above.
- ASTM C138
Cited by 3 of the calculators above.
- Approved Documents to the Building Regulations (England)
England (Wales, Scotland and Northern Ireland have their own). Cited by 1 of the calculators above.
- International Residential Code
United States. Cited by 1 of the calculators above.
Frequently asked questions
- How much concrete do I need for a slab?
- Multiply length, width and thickness for the net volume, add a waste factor for uneven ground and spillage, then round up to whole bags if you are buying bags. The concrete calculator does this in either unit system and prints the net volume and the volume with waste separately.
- How do I compare bags with a delivery?
- Turn one into the other. The bags-to-cubic-yards converter gives the volume a bag count makes, and the cubic-yards-to-bags converter gives the bags a volume needs, so a bagged job can be set against a delivery quote in the same unit. The concrete calculator prints both for a slab.
- Does concrete dry or cure?
- It cures: the cement reacts with water, so the surface must not lose that water early. The evaporation calculator applies the ACI 305R equation to judge the plastic shrinkage risk before the pour, and the curing compound and curing blanket calculators size the protection that follows.
- How much rebar does a slab need?
- That is a design decision, set by the load, the ground and the code, and no calculator here can replace the designer's detail. Once you have the bar size and spacing, the rebar calculator gives the lengths, the sticks to order and the weight.
- Why does my bag count differ from a calculator in another country?
- The bag calculator lists the bag sizes sold in the United States and the sizes sold in metric markets, and volume is in cubic yards in one setting and cubic metres in the other. Read the yield on your own bag, then check the calculator is set to your unit system.