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Concrete Calculator

Estimate how much concrete a slab needs — in cubic yards or cubic metres, and as a count of premix bags.

  • Answers as you type
  • Every formula cited
  • Calculated in your browser
SettingsSettings for this calculationUS
Market
Imperial · sales tax
Who is doing the work?

The standard allowance most suppliers and estimating guides assume for ordinary work.

The length of the slab or footing.

Measure the longest straight run of the area you're pouring.

Tools needed: Tape measure, Stakes and string for marking the pour area

The width of the slab or footing.

Measure perpendicular to the length.

Tools needed: Tape measure

How deep the concrete pour is.

4 inches (about 0.1 m) is standard for a patio or walkway. 6 inches (about 0.15 m) is common for a driveway that will carry vehicle weight.

Tools needed: Tape measure, Level

Extra concrete for spillage, uneven subgrade, and forming imprecision.

10% is standard. Order slightly more than the bare minimum — running short mid-pour with concrete already mixed is a serious problem.

Estimated concrete needed

1.358 yd³

High confidence
Volume (no waste)
1.23 yd³
Volume with waste factor
1.36 yd³
Cubic feet
36.67 ft³
80 lb bags needed
62 bags
Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

  • Standard formula: cubic yards = length (ft) x width (ft) x thickness (ft) / 27
  • An 80 lb bag of pre-mixed concrete yields approximately 0.6 cubic feet once mixed

Inputs used

Slab Length
10 ft
Slab Width
10 ft
Slab Thickness
4 in
Waste Factor (%)
10

Intermediate steps

Volume (no waste)
1.23 yd³
Volume with waste factor
1.36 yd³
Cubic feet
36.67 ft³
80 lb bags needed
62 bags
Final result1.36 yd³

What this calculation does not cover

  • Geometry is one rectangular prism: length x width x a single uniform thickness. Thickened edges, integral footings, haunches, steps, curbs and any non-rectangular outline are not in the figure, and nothing is subtracted for block-outs or openings. Take those off as separate volumes and add them.
  • It assumes a flat, compacted subgrade sitting at exactly the depth you entered. Ruts, soft spots, over-excavation and a base that dishes in the middle all take concrete the geometry never sees, and a flat waste percentage is not a measurement of that. On a rough base, check depth across the whole pour rather than trusting the allowance.
  • This is a volume take-off, not a structural decision. It accepts whatever thickness you type without sizing it, and says nothing about mix strength, aggregate size, air entrainment, fibre, or rebar and mesh. Slabs carrying vehicles, footings, and anything supporting a structure are a code and engineering question.
  • The bag count assumes an 80 lb (36 kg) bag yields about 0.6 cubic feet (17 litres) of mixed concrete, and rounds up to whole bags. Real yield shifts with the product and with how much water goes in, and no other bag size is converted for you.
  • The volume is not an order quantity. Ready-mix is sold in fixed increments with a minimum load and its own short-load charges, and concrete left in the drum, the chute or the pump line is not counted. The waste factor covers spillage and forming slop, not the plant's ordering rules.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Plan of the slab, 10′ by 10′.10′10′

Part of bigger jobs

This trade is one line of several job takeoffs. Run the whole job and every other trade comes back with it, off the same measurements.

Or plan the space itself: measure it once, doors and windows included, and this figure comes back worked out on that space, with what goes with it.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.0.1

Regulatory standards & verification citations2
  1. Standard formula: cubic yards = length (ft) x width (ft) x thickness (ft) / 27
  2. An 80 lb bag of pre-mixed concrete yields approximately 0.6 cubic feet once mixed
Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Tools and safety for this job

To place and finish concrete, erect formwork and saw-cut cured concrete. Generic types, no brands, no prices.

Protection this work requires

  • Cutting or grinding concrete, masonry, screed, tile or fibre-cement board releases respirable silica: cut wet or extract at the tool, and wear a P2/N95 respirator at minimum — a nuisance dust mask does not filter it.
  • Hardwood dust is a recognised carcinogen: extract at the tool and wear a P2/N95 respirator when cutting or sanding indoors.
  • Wet cement and lime burn skin and eyes painlessly until the damage is done: waterproof gloves to EN 374, safety glasses whenever the mix can splash, and never kneel in wet mix in permeable trousers.
  • Saws, grinders and breakers run above 85 dB, where hearing damage accumulates and does not recover: defenders or plugs for every cut, not just the long ones.
  • Breakers and grinders cause permanent nerve damage: limit continuous trigger time, keep hands warm, and stop if fingers tingle or blanch.
  • Boards, blocks and bagged material cause most lasting back injuries on small sites: two people or a lifter for full sheets, and never a bag on one shoulder up a ladder.
Show the 17 tools this job needs

Essential

  • Angle grinder

  • Bull float and edger

  • Circular saw

  • Claw hammer

  • Dust extractor or vacuum with a fine filter

  • Screed bar or rail

  • Shovel and spade

  • Spirit level

  • String line and pins

  • Tape measure

  • Wheelbarrow

Recommended

  • Chalk line

  • Cordless drill/driver

  • Floor or cut-off saw

  • Plate compactor

  • SDS rotary hammer

Optional

  • Power float

Also needed as materials: chalk refill, circular saw blades, cutting and diamond discs, diamond blades, drill and driver bits, SDS bits and chisels.

what each concrete tool is for, and the spec that decides which to buy where one does.

Code thresholds this tool can check

Code thresholds this tool can check

Checked for United States. Each check below names the body that published the limit it uses. Switching market re-runs them. This is not a code review and has no official standing.

These checks cover only the specific numeric limits listed below. They are not a complete code review: fire separation, egress, structural capacity and accessibility provisions are outside their scope, and only the handful of local amendments offered in the selector are modelled — your municipality may have others. Passing every check here does not make a design compliant. Final approval rests with your local building authority.

  • WITHIN LIMIT — Concrete floor slabs on ground: minimum 3.5 in (89 mm) thick.

    Slab thickness 4.00 in meets the 3.5 in IRC floor-slab minimum. Expansive soils are handled separately under IRC R403.1.8, and any slab carrying vehicles or point loads should be designed rather than taken from the code minimum.

    ICC · IRC R506.1

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

Called something else where you work? Cement vs concrete · Kerb / curb · Slump and consistence · Spalling and scaling — the term in each market, how close the equivalence really is, and the standard that governs it.

Still deciding? Concrete Slab vs Pavers · Bagged Concrete vs Ready-Mix · Shed on Skids vs Concrete Slab — the factors that actually differ, with no invented prices.

Already have some? How big a slab will a yard of concrete pour? · How big a slab will my bags of concrete make?

Worked example: Garden room slab — step 7 of 9

Worked for these jobs: A garden shed base, in cubic metres · A rectangular slab, in cubic yards

Already gone wrong? The edges of my concrete slab have lifted or curled · A white powder or bloom keeps appearing on my concrete floor · My concrete floor keeps producing dust

The data behind it: Production rates by operation

How to calculate concrete in 5 steps

  1. Slab LengthThe length of the slab or footing.
  2. Slab WidthThe width of the slab or footing.
  3. Slab ThicknessHow deep the concrete pour is.
  4. Waste Factor (%)Extra concrete for spillage, uneven subgrade, and forming imprecision.
  5. Read the resultThe tool computes the result from those figures and shows the formula, its sources, and a confidence rating alongside it.

Frequently asked questions

Should I order exactly this amount from a ready-mix truck?
Order slightly more if you're unsure — ready-mix trucks usually charge a short-load fee for small orders anyway, and running short mid-pour is far worse than having a little extra.
How thick should my slab be?
4 inches (~0.1 m) is standard for patios, walkways, and shed floors. 6 inches (~0.15 m) is common for driveways carrying vehicle weight. Check local code for structural slabs.
Does this calculator account for rebar or wire mesh?
No — this estimates concrete volume only. Reinforcement is a separate material and structural decision, especially for driveways and load-bearing slabs.
Why 80 lb bags specifically?
80 lb bags are the most common size sold at hardware stores for DIY pours. If your bags are a different size, scale the bag count by the ratio of volumes.
Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.