Why proportion by absolute volume instead of by mass?

Because a kilogram of cement and a kilogram of sand do not take up the same space, and concrete is sold and placed by volume. Cement has a specific gravity near 3.15 and sand near 2.63, so the same mass of cement occupies about a sixth less room. Proportioning by mass would leave the batch yielding whatever it happened to yield, which is exactly the failure ASTM C138's relative yield check exists to catch. The absolute volume of an ingredient is the volume of the SOLID material with no voids between the grains — and that is the right measure here because in hardened concrete there are no voids between the grains: the paste has filled them. Add up the absolute volumes of everything you have chosen, subtract from the batch volume, and what remains is the room the sand has. That is the whole method.

Why is specific gravity an input rather than a constant?

Because it is a property of YOUR materials, and the error goes straight into the sand. Portland cement is close to 3.15 anywhere in the world, but a binder blended with fly ash (near 2.3) or slag (near 2.9) is materially lighter, and a mix at thirty per cent replacement occupies noticeably more volume per kilogram than the default assumes. Aggregate is worse: normal crushed rock runs 2.6 to 2.75, but lightweight aggregate can be under 2.0 and heavyweight well over 3.0, and those are different concretes entirely. Because the fine aggregate is computed as a remainder, every specific gravity error in the other ingredients accumulates into it — get the coarse aggregate's figure wrong by two per cent and the sand absorbs the whole discrepancy. The figures belong on your supplier's test certificate, measured under ASTM C127 and C128.

What does it mean when the calculator says the design does not fit?

That the ingredients already chosen fill or overflow the batch volume, leaving no room for sand — so the mix cannot be made as written. It is not an error in the arithmetic; it is the arithmetic telling you something is wrong upstream. The two usual causes are too much coarse aggregate, often from reading the volume table against the wrong fineness modulus or confusing a dry-rodded bulk density with a specific gravity, and an air content specified for freeze-thaw exposure that nobody allowed room for. Entrained air is real volume: moving from two per cent entrapped to six per cent entrained takes forty litres out of every cubic metre, and that forty litres comes off the sand. The fix is to reduce the coarse aggregate or revisit the water content, not to squeeze the sand.

Does this replace a trial batch?

No, and ACI 211.1 is explicit that nothing does. A mix design calculated on paper is a starting point built from table values and typical properties; the standard's own procedure is to mix a trial batch, measure its slump, air content, density and strength, and adjust from what the batch actually did. The adjustment is usually proportional — if the trial yielded less than the design volume, every ingredient scales up by the same factor, which is what the trial batch yield adjustment page does. There are also things this arithmetic cannot see at all: how the particular sand's grading affects workability, how an admixture changes the water demand, and how the materials behave together at the temperature they will actually be mixed at. Treat the figure here as the number you take to the trial, not the number you take to the pour.

Materials & Quantities

Concrete Mix Design Calculator — ACI 211.1 Absolute Volume Method

Fine aggregate for a concrete mix by ACI 211.1 absolute volume, from the cement, water, coarse aggregate and air chosen, with a check the design fits.

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Batch volume

The volume of finished concrete this batch must produce.

One cubic metre is the usual basis for a mix design, and every other quantity below must be for the SAME volume. Design at a unit volume and scale afterwards rather than designing at truck size — the arithmetic is identical and the unit figures are what a specification is written in.

Cementitious material

Total cement plus any supplementary cementitious materials.

The whole binder, because the water-cement ratio is written against the total cementitious content rather than against portland cement alone. Where a blend is used, its specific gravity is a weighted average and not 3.15 — a mix at thirty per cent fly ash is materially lighter than one at none.

Mixing water

The mixing water for the batch, from the table or from the target ratio.

Water is the one ingredient whose mass and volume are the same number, because specific gravity is defined against it. This is the water in the MIX, not the water on the aggregate — free moisture on a wet stockpile counts toward it and has to be subtracted before batching.

Coarse aggregate, SSD

Coarse aggregate at saturated surface-dry, for this batch volume.

ACI 211.1 selects this from the dry-rodded bulk density and a table of coarse aggregate volume per unit volume of concrete, indexed by maximum aggregate size and by the fine aggregate's fineness modulus. Take it from the standard; this page starts once you have it.

Air content

Total air as a percentage of the batch volume.

Entrapped air alone is roughly half a per cent to three per cent depending on aggregate size. Deliberately entrained air for freeze-thaw exposure is far more — commonly four to seven and a half per cent — and it occupies real volume that the sand does not get. Air specified and not allowed for is one of the commonest reasons a designed mix will not yield.

Cementitious specific gravity

3.15 for portland cement; lower for a blend.

Portland cement is close to 3.15 everywhere. Blends are not: fly ash is near 2.3 and slag near 2.9, so a binder containing them has a weighted average well below 3.15 and takes up more room for the same weight than the default assumes. The figure itself is a ratio and carries no units — it is how many times denser the solid is than water.

Coarse aggregate specific gravity, SSD

A measured property of the source, from ASTM C127.

Most natural crushed rock and gravel falls between 2.6 and 2.75, but lightweight and heavyweight aggregates are far outside that and the whole design changes with them. Use the figure on your supplier's test certificate rather than a typical value where the mix matters.

Fine aggregate specific gravity, SSD

A measured property of the sand, from ASTM C128.

This one converts the leftover VOLUME into the sand MASS you actually batch, so an error here lands entirely on the sand and shows up as a mix that does not yield. Manufactured sands frequently differ from natural sands out of the same region.

Fine aggregate needed, SSD

1,770 lb

Medium confidence

Water-cement ratio 0.500, fresh density 148 pcf. The sand fills what is left of the batch after cement, water, coarse aggregate and air have taken their absolute volumes — so every error above lands here. Prove it with a trial batch before it is used.

Cement, absolute volume: 3.92 ft³
Water, absolute volume: 6.17 ft³
Coarse aggregate, absolute volume: 13.84 ft³
Air: 0.71 ft³
Left for fine aggregate: 10.8 ft³
Total batch mass: 5,242.75 lb

Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

ACI 211.1, Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete — the absolute-volume method, in which every ingredient's solid volume is its mass divided by its specific gravity and the fine aggregate fills the remainder of the unit volume
The water content, air content, water-cement ratio and coarse aggregate volume that feed this arithmetic are read from ACI 211.1's own tables against your slump, maximum aggregate size, strength and exposure. Those tables are not reproduced here — take them from the standard
Specific gravities are inputs, not constants: 3.15 is typical for portland cement but supplementary cementitious materials differ sharply (fly ash near 2.3, slag near 2.9), and aggregate specific gravity is a measured property of the source under ASTM C127 and C128
All aggregate quantities are on a SATURATED SURFACE-DRY basis, as ACI 211.1 designs them. Correcting to the moisture of a real stockpile is a separate step and has its own page

Inputs used

Batch volume: 265 gal
Cementitious material: 770 lb
Mixing water: 385 lb
Coarse aggregate, SSD: 2315 lb
Air content: 2
Cementitious specific gravity: 3.15
Coarse aggregate specific gravity, SSD: 2.68
Fine aggregate specific gravity, SSD: 2.63

Intermediate steps

Cement, absolute volume: 3.92 ft³
Water, absolute volume: 6.17 ft³
Coarse aggregate, absolute volume: 13.84 ft³
Air: 0.71 ft³
Left for fine aggregate: 10.8 ft³
Total batch mass: 5,242.75 lb

Final result1,772.75 lb

Confidence note: Water-cement ratio 0.500, fresh density 148 pcf. The sand fills what is left of the batch after cement, water, coarse aggregate and air have taken their absolute volumes — so every error above lands here. Prove it with a trial batch before it is used.

What this calculation does not cover

This is the arithmetic half of ACI 211.1, not the whole practice. The water content, the air content, the water-cement ratio and the coarse aggregate volume are read from the standard's tables against your slump, maximum aggregate size, strength and exposure class, and they are not reproduced here.
Every quantity is SATURATED SURFACE-DRY. Real stockpiles are wetter or drier, and batching these figures against damp aggregate puts the mix wrong in two directions at once — the weights move by TOTAL moisture and the water by FREE moisture. Correct for it before batching.
A mix design is a starting point and the standard says so: it is proved by a TRIAL BATCH, measured for slump, air, density and strength, and adjusted. Nothing computed here has been tested, and the specific gravities it rests on are properties of your materials rather than of concrete in general.
Specific gravity is not bulk density. The absolute volume of an aggregate excludes the voids between the grains, which is why a figure taken from a dry-rodded bulk density gives a badly wrong answer here.
Admixtures are not accounted for. Water reducers, plasticisers and retarders change the water demand this arithmetic takes as given, and a high-range water reducer changes it enough to invalidate the water content the table supplied.
Nothing here checks durability. A mix can be perfectly proportioned by volume and still be wrong for its exposure — the water-cement ratio and the air content are the durability decisions, and both arrive here already made.

Estimated cost — your price

Price per lb ($)

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.

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 2026-09-15 · v1.0.0

Regulatory standards & verification citations4

ACI 211.1, Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete — the absolute-volume method, in which every ingredient's solid volume is its mass divided by its specific gravity and the fine aggregate fills the remainder of the unit volume
The water content, air content, water-cement ratio and coarse aggregate volume that feed this arithmetic are read from ACI 211.1's own tables against your slump, maximum aggregate size, strength and exposure. Those tables are not reproduced here — take them from the standard
Specific gravities are inputs, not constants: 3.15 is typical for portland cement but supplementary cementitious materials differ sharply (fly ash near 2.3, slag near 2.9), and aggregate specific gravity is a measured property of the source under ASTM C127 and C128
All aggregate quantities are on a SATURATED SURFACE-DRY basis, as ACI 211.1 designs them. Correcting to the moisture of a real stockpile is a separate step and has its own page

Which documents these citations point at

Standards referenced: ACI 211.1 (American Concrete Institute, United States); ASTM C127 (ASTM International, United States).

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.

Now that you have the number

These guides cover the work this quantity is for.

Designing a Concrete Mix and Reading the Submittal

How to calculate concrete mix design — ACI 211.1 absolute volume method in 9 steps

Batch volumeThe volume of finished concrete this batch must produce.
Cementitious materialTotal cement plus any supplementary cementitious materials.
Mixing waterThe mixing water for the batch, from the table or from the target ratio.
Coarse aggregate, SSDCoarse aggregate at saturated surface-dry, for this batch volume.
Air contentTotal air as a percentage of the batch volume.
Cementitious specific gravity3.15 for portland cement; lower for a blend.
Coarse aggregate specific gravity, SSDA measured property of the source, from ASTM C127.
Fine aggregate specific gravity, SSDA measured property of the sand, from ASTM C128.
Fine aggregate needed, SSDThe tool computes the fine aggregate needed, SSD from those figures and shows the formula, its sources, and a confidence rating alongside it.

Fine aggregate needed, SSD by batch volume

Page defaults, not your figures above.

Batch volume	Fine aggregate needed, SSD (lb)
200 gal	371
300 gal	2,522
400 gal	4,673
500 gal	6,824

Frequently asked questions

Why proportion by absolute volume instead of by mass?: Because a kilogram of cement and a kilogram of sand do not take up the same space, and concrete is sold and placed by volume. Cement has a specific gravity near 3.15 and sand near 2.63, so the same mass of cement occupies about a sixth less room. Proportioning by mass would leave the batch yielding whatever it happened to yield, which is exactly the failure ASTM C138's relative yield check exists to catch. The absolute volume of an ingredient is the volume of the SOLID material with no voids between the grains — and that is the right measure here because in hardened concrete there are no voids between the grains: the paste has filled them. Add up the absolute volumes of everything you have chosen, subtract from the batch volume, and what remains is the room the sand has. That is the whole method.
Why is specific gravity an input rather than a constant?: Because it is a property of YOUR materials, and the error goes straight into the sand. Portland cement is close to 3.15 anywhere in the world, but a binder blended with fly ash (near 2.3) or slag (near 2.9) is materially lighter, and a mix at thirty per cent replacement occupies noticeably more volume per kilogram than the default assumes. Aggregate is worse: normal crushed rock runs 2.6 to 2.75, but lightweight aggregate can be under 2.0 and heavyweight well over 3.0, and those are different concretes entirely. Because the fine aggregate is computed as a remainder, every specific gravity error in the other ingredients accumulates into it — get the coarse aggregate's figure wrong by two per cent and the sand absorbs the whole discrepancy. The figures belong on your supplier's test certificate, measured under ASTM C127 and C128.
What does it mean when the calculator says the design does not fit?: That the ingredients already chosen fill or overflow the batch volume, leaving no room for sand — so the mix cannot be made as written. It is not an error in the arithmetic; it is the arithmetic telling you something is wrong upstream. The two usual causes are too much coarse aggregate, often from reading the volume table against the wrong fineness modulus or confusing a dry-rodded bulk density with a specific gravity, and an air content specified for freeze-thaw exposure that nobody allowed room for. Entrained air is real volume: moving from two per cent entrapped to six per cent entrained takes forty litres out of every cubic metre, and that forty litres comes off the sand. The fix is to reduce the coarse aggregate or revisit the water content, not to squeeze the sand.
Does this replace a trial batch?: No, and ACI 211.1 is explicit that nothing does. A mix design calculated on paper is a starting point built from table values and typical properties; the standard's own procedure is to mix a trial batch, measure its slump, air content, density and strength, and adjust from what the batch actually did. The adjustment is usually proportional — if the trial yielded less than the design volume, every ingredient scales up by the same factor, which is what the trial batch yield adjustment page does. There are also things this arithmetic cannot see at all: how the particular sand's grading affects workability, how an admixture changes the water demand, and how the materials behave together at the temperature they will actually be mixed at. Treat the figure here as the number you take to the trial, not the number you take to the pour.

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.