Concrete Mix Ratio Calculator
Split a volume of concrete into cement, sand and aggregate at a given ratio.
Last reviewed September 19, 2026
Result
Buy 5 bagsEstimate
No allowance is added. Site mixing wastes more than ready mix, between spillage, material left in the mixer and a batch that ends up too wet, so add your own margin on top, especially on the cement.
- Cement
- 534 lb (242.2 kg)Estimate
- Cement volume
- 5.94 ft³Estimate
- Sand
- 11.88 ft³ (0.44 yd³)Estimate
- Aggregate
- 23.76 ft³ (0.88 yd³)Estimate
- Total dry volume
- 41.58 ft³ (1.54 yd³)Estimate
https://calcgallery.com/concrete/concrete-mix-ratio-calculator/
Results are estimates for planning only. Actual needs vary with site conditions, products and workmanship. Always confirm quantities with your supplier and follow local building codes and manufacturer instructions. Read the full disclaimer
How to use it
- Enter the finished volume of concrete you need. Take it from the slab or column calculator.
- Pick a mix ratio. 1:2:4 is the general purpose default.
- Choose the cement bag size you can buy.
- Read the cement bags, and the sand and aggregate volumes.
How it is calculated
A nominal mix splits a dry volume between three ingredients in proportion:
dry volume = wet volume × 1.54
cement volume = dry × cement parts ÷ total parts
cement mass = cement volume × bulk density
bags = ceil(cement mass ÷ bag size)Sand and aggregate follow the same split. The 1.54 factor is the one that catches people out: a cubic metre of finished concrete needs about 1.54 cubic metres of loose dry material, because mixing closes up the air between the particles and the water fills what is left.
Cement is then converted from volume to mass, because it is sold by the bag rather than by the bucket. Sand and aggregate stay as volumes, which is how they are delivered.
A note on strength
Nominal volumetric mixes like 1:2:4 are rules of thumb that predate modern mix design. They give reasonable general purpose concrete when the materials are good and the water is controlled, and they are entirely adequate for a shed base or a path.
They are not a specification. A mix ratio says nothing about the strength you will actually get, which depends on the water-cement ratio, the cement type, the aggregate grading and shape, and how the concrete is compacted and cured. Two batches at the same ratio can differ enormously.
Anything carrying structural load, anything exposed to freeze-thaw or chemicals, and anything an inspector will look at needs a designed mix to a specified strength class. That usually means ready-mix, and a delivery ticket.
Practical tips
Measure by volume with the same container. A bucket for everything. Mixing a shovel of cement with a bucket of sand gives you whatever ratio the shovel happened to hold that time.
Allow for bulking in damp sand. Damp sand takes up noticeably more volume than dry sand, sometimes 20 per cent or more, so measuring damp sand by volume quietly leans the mix. It settles back as soon as it is wetted in the mixer.
Add water last and slowly. It is the one ingredient you cannot take back out, and every extra litre costs strength. Stop at the workability you actually need.
Mix in consistent batches. Ratios only hold if every batch is the same. Work out your per-batch quantities once and stick to them.
Cure it. Concrete gains strength by hydration, not by drying. Keep it damp and covered for several days. Letting a slab dry out in the sun on day one loses more strength than any ratio choice will gain.
With your numbers
- Dry volume = 27 ft³ × 1.54 = 41.58 ft³
- Cement = 41.58 ft³ × 1 ÷ 7 = 5.94 ft³, which is 534 lb
- Sand 11.88 ft³, aggregate 23.76 ft³, at 2 and 4 parts
- Bags = cement mass ÷ bag size, rounded up to 6
Quick reference
No allowance is added. Site mixing wastes more than ready mix, between spillage, material left in the mixer and a batch that ends up too wet, so add your own margin on top, especially on the cement.
| Job | Cement bags to buy |
|---|---|
| 1 m³ at 1:2:4 | 7 |
| 1 m³ at 1:1.5:3 | 9 |
| 1 m³ at 1:3:6 | 5 |
| 0.5 m³ at 1:2:4 | 4 |
| 2 m³ at 1:2:4 | 13 |
| 1 yd³ at 1:2:4 | 6 |
| 2 yd³ at 1:2:4 | 12 |
| 1 yd³ at 1:3:6 | 4 |
Common questions
- How much cement do I need for 1 cubic metre of concrete?
- About seven 50 kg bags at a 1:2:4 mix, which is 0.22 m³ or 316.8 kg of cement, with 0.44 m³ of sand and 0.88 m³ of aggregate. A richer 1:1.5:3 mix needs nine bags.
- What does 1:2:4 mean?
- One part cement to two parts sand to four parts coarse aggregate, measured by volume. It is the traditional general purpose nominal mix. 1:1.5:3 is stronger and used where more strength is wanted; 1:3:6 is leaner and used for mass fill and foundations.
- Why is the dry volume more than the wet volume?
- Because loose sand and aggregate have air between the particles, and mixing packs them together. The dry ingredients occupy roughly 1.54 times the volume of the concrete they produce. Skipping that factor is why site-mixed batches come up short.
- How much water should I add?
- Not something to take from a ratio calculator. Water content controls strength more than anything else, and the right amount depends on the aggregate's moisture, the cement and the workability you need. Too much water is the commonest cause of weak concrete. Add it gradually to the workability you need and no further.
- Can I use this for structural concrete?
- No. Nominal volumetric mixes are general guidance for non-structural work: a shed base, a path, a post, bedding. Anything structural needs a designed mix with a specified strength class, and usually ready-mix with a delivery ticket you can show an inspector.
- Is it worth site mixing at all?
- Below about half a cubic metre, usually yes. Above a cubic metre, ready-mix is almost always cheaper once you count the hire, the labour and the waste, and it is far more consistent. Site mixing a large slab in batches also risks cold joints between loads.