Concrete & Mortar Mix Calculator
Work out the cement, sand, gravel and water for a concrete or mortar mix. Pick a ratio such as 1:2:3, 1:2:4 or 1:4 to get bags of cement and the sand and stone by volume or weight.
How to Use
- Choose concrete (cement, sand and gravel) or mortar (cement and sand).
- Enter the volume you need, from the concrete calculator or your own measurements.
- Pick the mix ratio and the cement bag size you can buy.
- Set the water-cement ratio: 0.45 to 0.5 for strong, durable concrete; more water makes it easier to work but weaker.
- Read the bags of cement, the sand, the gravel and the water; the steps also show what one bag makes.
Worked Example
One cubic metre of 1:2:4 concrete, 50 kg bags, water-cement ratio 0.5. Dry volume = 1 × 1.54 = 1.54 m³. The ratio has 1 + 2 + 4 = 7 parts. Cement = 1.54 × 1/7 = 0.22 m³ × 1,440 kg/m³ = 316.8 kg, which is 6.34 bags, so buy 7 bags. Sand = 1.54 × 2/7 = 0.44 m³ (about 0.70 t). Gravel = 1.54 × 4/7 = 0.88 m³ (about 1.32 t). Water = 0.5 × 316.8 = 158 litres.
In US units: one cubic yard of 1:2:3 with 94 lb bags takes 283 kg (623 lb) of cement, so 6.6, call it 7 bags; 13.9 ft³ of sand, 20.8 ft³ of gravel and 37 gallons of water. That is the familiar “six to seven bags a yard”.
The common mistake: batching the wet volume. Measuring out 1 m³ of loose sand, gravel and cement in the ratio gives only about 0.65 m³ of concrete, because the fine grains fill the voids between the coarse ones. Without the 1.54 factor, you run out a third of the way through the pour.
Show Work
Formulas
Nominal Mixes and the Water-Cement Ratio
Ratios like 1:2:4 are nominal mixes, batched by volume with a bucket or a shovel count, and they have been used on building sites since Portland cement was patented by Joseph Aspdin in 1824. They are simple and reliable for small work. Ready-mix plants instead batch by weight to a design mix tested for a target strength, which is why a truck ticket says 4,000 psi or C25/30 rather than a ratio.
In 1918 Duff Abrams showed that concrete strength depends mostly on one number, the ratio of water to cement. Halving the water roughly doubles the strength, as long as the mix can still be placed and compacted. That is why adding water on site to make concrete flow more easily is the most common way strong concrete is made weak.
About This Calculator
This calculator turns a volume of concrete or mortar and a nominal mix ratio into bags of cement, sand and gravel by volume and weight, and water, in US or metric units, and shows what a single bag of cement makes. It draws the batch as buckets so the proportions are easy to follow on site.
Everything runs in your browser; nothing is sent anywhere. Figures are for dry, loose materials; damp sand bulks up by 20 to 30% and holds water, so measure it loosely and hold back some of the water. For structural work, use a tested design mix.
Related calculators: Concrete Calculator, Brick Calculator, and Gravel Calculator.
Frequently Asked Questions
How much cement, sand and gravel for 1 cubic metre of concrete?
At 1:2:4, about 317 kg of cement (7 bags of 50 kg), 0.44 m³ of sand and 0.88 m³ of gravel, with about 158 litres of water. At 1:2:3, a richer mix, it is 370 kg of cement, 0.51 m³ of sand and 0.77 m³ of gravel.
Why multiply by 1.54?
Dry materials have air between the grains. When they are wetted and mixed, the sand fills the gaps in the gravel and the cement fills the gaps in the sand, so the finished concrete is about a third smaller than the pile of dry ingredients. Multiplying by 1.54 for concrete (1.33 for mortar, which has no gravel) gives the dry volume to batch.
What mix ratio should I use?
1:2:4 is the everyday mix for footings, foundations and paths, roughly 15 MPa (2,200 psi). 1:2:3 and 1:1.5:3 are richer, roughly 20 MPa (3,000 psi), for slabs, driveways and anything exposed to frost. 1:3:6 is lean concrete, about 10 MPa, for blinding and mass fill. Actual strength depends on the water and the curing. For mortar, 1:3 is strong, 1:4 is general brickwork and 1:5 or 1:6 is for softer bricks, usually with lime or plasticiser.
How much water should I add?
Water is set by the water-cement ratio, the weight of water divided by the weight of cement. At 0.5, a 50 kg bag takes 25 litres and a 94 lb bag 5.6 US gallons. Add part of it, mix, then add the rest slowly; extra water makes concrete easier to place but weaker and more prone to cracking. Wet sand already holds some of it.
How much concrete does one bag of cement make?
At 1:2:3, one 94 lb bag of Portland cement with about 2.1 ft³ of sand and 3.1 ft³ of gravel makes about 4.1 ft³ of concrete, 0.15 yd³. A 50 kg bag at 1:2:4 makes about 0.16 m³.
How do I use the Concrete & Mortar Mix Calculator?
Just type your numbers. The answer shows up right away — there is no button to press. Change anything and it updates by itself.
Is it free? Does it work without internet?
Yes to both. It is free with no sign-up, and once the page has loaded it keeps working even with no internet.
Where does my data go?
Nowhere — every calculation runs on your own device. Nothing you enter is uploaded, logged, or stored.
Common Use Cases
One cubic metre
1:2:4 with 50 kg bags: 7 bags of cement, 0.44 m³ of sand, 0.88 m³ of gravel, 158 L of water.
One cubic yard
1:2:3 with 94 lb bags: 7 bags, 13.9 ft³ of sand, 20.8 ft³ of gravel, 37 gallons of water.
Mortar for brickwork
0.5 m³ of 1:4 mortar: 192 kg of cement (4 bags of 50 kg) and 0.53 m³ of sand.
A small pad
10 ft³ of 1:2:3: 3 bags of cement, 5.1 ft³ of sand and 7.7 ft³ of gravel.
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