Concrete Mix Design Calculator
Work out cement, sand, gravel and water per cubic metre from the target grade and water-cement ratio.
Quick answer
With the default inputs: Target grade C30 · Cement strength class 42.5 · Max aggregate size 31.5 etc.Cement content 377 kg/m³
Edit the inputs below to recalculate.Inputs
Result
Cement content
377kg/m³
| Target mean strength | 38.2MPa |
| Water-cement ratio | 0.527 |
| Water | 199kg/m³ |
| Sand | 693kg/m³ |
| Gravel | 1131kg/m³ |
| Ratio cement : sand : gravel | 1 : 1.84 : 3.00 |
| Sand per 50 kg cement | 91.9kg |
| Gravel per 50 kg cement | 150.0kg |
| Water per 50 kg cement | 26.4kg |
Estimated by the volumetric method of JGJ 55, without admixtures. A laboratory mix design and trial batches are mandatory before construction.
Reverse: known result, work out one input
Enter a target result; the other inputs stay fixed and this one is worked out.
Formula
| Target mean strength | fcu,0 = fcu,k + 1.645σ (σ = 5.0 MPa) |
| Effective cement strength | fce = γc × cement class |
| Water-cement ratio | W/C = 0.53fce ÷ (fcu,0 + 0.53×0.20×fce) |
| Cement content | mc = mw ÷ (W/C) |
| Total aggregate | ms + mg = 2400 − mw − mc |
| Sand | ms = (ms+mg) × sand ratio |
C30 with 42.5 class cement, 31.5 mm aggregate, 90 mm slump and 38% sand: W/C 0.527, water 199 kg, cement 377 kg, sand 693 kg, gravel 1131 kg — a ratio of 1 : 1.84 : 3.00.
Reference mixes by grade (per m³, medium sand, 31.5 mm aggregate)
| Grade | W/C | Cement (kg) | Sand (kg) | Gravel (kg) | Water (kg) |
|---|---|---|---|---|---|
| C20 | 0.62 | 290 | 750 | 1150 | 180 |
| C25 | 0.57 | 320 | 715 | 1155 | 182 |
| C30 | 0.53 | 377 | 693 | 1131 | 199 |
| C35 | 0.48 | 400 | 680 | 1125 | 192 |
| C40 | 0.44 | 440 | 665 | 1118 | 194 |
How to work it out
- Set the target strength: fcu,o = fcu,k + 1.645σ, with σ from grade and site control (5.0 MPa is typical for C30).
- Set the water-binder ratio from target strength and actual cement strength, then check it against the durability ceiling.
- Set water content from slump and maximum aggregate size — 160-185 kg/m³ for pumped concrete.
- Set sand ratio: 38-45% for pumping, 2-3% higher for crushed than rounded aggregate, 2% more again for fine sand.
- Compute the batch by absolute volume, then prove it with a trial mix — never take it straight to site.
Where it goes wrong
- Using the laboratory mix as the site mix — aggregate arrives wet and must be corrected for moisture, or the water-binder ratio is simply wrong.
- Checking strength but not durability — the water-binder ratio has a ceiling (0.60 in mild exposure) that strength alone does not satisfy.
- Guessing the sand ratio — 2% low on a pumped mix is enough to block the line.
Material and cost
Mix design drives cost directly: 20 kg less cement per cubic metre saves about 9 per m³ at 450 per tonne, which is 90,000 on a 100,000 m³ project. But cutting cement costs strength and durability, so it has to stay inside trial-mix results and code limits.
On site
- Test aggregate moisture on every delivery — during the wet season it can change twice a day.
- Fly ash and slag cut cost but reduce early strength, so striking times must move out accordingly.
- Keep the trial cubes for the full 28 days; extrapolating from 7-day results is out by up to 15%.
Basis
- JGJ 55-2011 Specification for mix proportion design of ordinary concrete
- GB 50204-2015 Code for acceptance of concrete structures, Section 7.3
- GB 175-2007 Common Portland cement (strength classes and requirements)
FAQ
How do water-cement ratio and slump relate?
Water-cement ratio governs strength; slump governs workability, and the two pull against each other. For a given grade, a wetter mix either means more water (lower strength) or a superplasticiser (same strength, higher cost). Adding water on site is the worst trade: you save a few yuan of admixture and lose a whole strength grade.
Why is my cement figure higher than the ready-mix supplier's?
Suppliers substitute fly ash, slag and admixtures, cutting cement by 15-30% while keeping total binder constant. This calculator assumes pure cement. With 20% fly ash, multiply cement by 0.8 and add fly ash at about 0.25 times the cement mass to hold the binder content.
What sand ratio should I use?
Sand ratio trades workability against strength: too high loses strength, too low segregates and blocks the pump. Typical ranges for crushed stone: 33-38% at 30-70 mm slump, 38-43% at 70-120 mm, 40-45% for pumped concrete at 120-180 mm. Use the low end for fine sand and the high end for coarse sand; manufactured sand runs 2-3 points higher than natural sand.
Cite this page
Use this format in reports, method statements or coursework. The link is permanent.
Building Calculator. Concrete Mix Design Calculator. 2026-10-25. https://jianzhujisuan.com/en/concrete-mix-ratio
Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.