Concrete Mix Ratio Calculator
Split a concrete volume into cement, sand, and aggregate using your own volumetric ratio, such as 1:2:3.
Content updated September 14, 2026
This splits a volume you already have across your own ratio — it does not choose a ratio, strength, or water amount for you. PCA’s history traces the arbitrary volumetric method (1:2:3) back to 1918; modern structural work is normally weight- and water-cement-ratio designed. Use a nominal ratio like this only for non-structural or small work, and verify strength requirements with a qualified professional for anything load-bearing.
Split a concrete volume you already have — from a slab, footing, or column calculator, or entered directly — into cement, sand, and coarse-aggregate shares using a volumetric mix ratio you choose, such as 1:2:3 or 1:2:4.
This proportions a volume; it does not select a ratio, a strength, or a water amount for you. Portland Cement Association's own history traces this "arbitrary volumetric method" back to 1918, before weight- and water-cement-ratio design became standard for structural work.
The Concrete Mix Ratio formula
Total parts = cement + sand + aggregate parts · order volume = target volume × (1 + allowance% ÷ 100) · material volume = order volume × (material parts ÷ total parts) · material weight = material volume × bulk densityTarget volume is converted to cubic feet before splitting · cement is reported as bags using your entered bag yield · sand and aggregate weight use your entered bulk density in lb/ft³.
Worked example
A 1:2:3 ratio (6 total parts) for a 1 yd³ (27 ft³) target with a 10% allowance gives an order volume of 29.7 ft³: 4.95 ft³ of cement (8.25 bags at 0.6 ft³/bag, rounding up to 9), 9.9 ft³ of sand (990 lb at 100 lb/ft³), and 14.85 ft³ of coarse aggregate (1,559.25 lb at 105 lb/ft³).
Assumptions, rounding, and limitations
Assumptions
- Cement, sand, and aggregate parts are proportional shares of the entered ratio, not fixed absolute units.
- The entered contingency percentage is applied to the target volume before splitting into materials.
- Sand and aggregate weight use the bulk density you enter; cement bag count uses the bag yield you enter.
- Water is not modeled — the ratio and this calculator cover only cement, sand, and coarse aggregate.
Rounding: Volume and weight math retain floating-point precision. Displayed figures show up to three decimal places; cement bag count always rounds the exact quotient upward to a whole bag.
Limitations
- Does not select a mix ratio, target strength, or water-cement ratio, and is not a substitute for a designed mix on structural or load-bearing work.
- Does not account for aggregate moisture content, bulking, or compaction, all of which change real bulk density.
- The result is a planning estimate and should be checked against your own mix design, supplier guidance, or a qualified professional for anything structural.
Sources
- Design and Control of Concrete Mixtures — Chapter 9: Designing and Proportioning Normal Concrete Mixtures — Portland Cement Association
- NIST Guide to the SI, Appendix B: Conversion Factors — National Institute of Standards and Technology
Parts are relative, not fixed units
A 1:2:3 ratio means 1 part cement to 2 parts sand to 3 parts coarse aggregate by volume — the parts are proportional shares of the total, not a specific unit of measure, so the same ratio works whether the target volume is 1 cubic foot or 10 cubic yards.
The calculator adds each part's parts count, divides your target volume across those parts by fraction, then applies your chosen contingency allowance to the whole before splitting.
Weight comes from your own bulk density
Sand and aggregate weight are computed from a bulk density you enter, because moisture content, compaction, and material source change real bulk density substantially — there is no single correct value to assume.
Cement is reported in bags using a bag yield you enter, matching the same pattern as the concrete slab calculator's bag count, so the packaging you actually have determines the count.
Frequently asked questions
▶How do I split a concrete volume by a mix ratio?
Add the ratio's parts together to get a total, divide your target volume (plus any allowance) into that many equal shares, then multiply by each material's own number of parts.
▶What does a ratio like 1:2:3 mean?
It states cement to sand to coarse aggregate by volume — 1 part cement, 2 parts sand, 3 parts coarse aggregate. PCA's own history traces this style of proportioning to 1918.
▶Does this tell me which ratio to use?
No. You choose the ratio. Structural or load-bearing concrete should normally be specified by required strength and a water-cement ratio, not an arbitrary volumetric ratio — get that from an engineer or ready-mix producer.
▶Why do I have to enter sand and aggregate density myself?
Bulk density varies with moisture, gradation, and material source — often by 10% or more — so a universal assumption would misstate the real weight. Use the figure from your own supplier.
▶Does this calculate water?
No. Water amount depends on a target water-cement ratio, admixtures, and site conditions, all of which are outside this calculator's scope — follow your mix design or product instructions.
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Open calculator →Disclaimer: Concrete Mix Ratio Calculator results are estimates for general information and education only, and are not financial, tax, legal or medical advice. Verify important decisions with a qualified professional.