Cement Calculator
Mixing your own concrete or mortar means getting three quantities right: cement, sand and aggregate. This cement calculator splits any volume into its ingredients for the mix ratio you choose.
Enter the finished volume you need, pick a mix — from lean 1:3:6 concrete to strong 1:1.5:3 or masonry mortar — and get bags of cement plus cubic metres of sand and gravel.
Enter valid values to see the results.
Formula
Dry ingredients occupy about 54% more volume than the cured mix, so wet volume is multiplied by 1.54 before splitting by ratio. A 50 kg cement bag is about 0.035 m³; a 94 lb bag is about 1 ft³. Water is estimated at 25 litres per 50 kg bag (water-cement ratio ≈ 0.5).
How to measure
- First calculate the wet volume of your element with the Concrete Calculator, then enter it here.
- Choose the mix ratio required by your project — structural slabs need richer mixes than garden paths.
- For mortar (bricklaying, plaster), choose a ratio with no gravel part.
Worked example
Practical tips
- Use fresh cement — it loses about 20% of its strength after 3 months of storage, even in dry conditions.
- Measure ingredients by volume with the same bucket for consistency; never estimate by shovelfuls.
- Add water gradually: a mix that is too wet is easy to pour but cures weak and cracks.
- Mix only what you can place within 60–90 minutes, less in hot weather.
Waste allowance
The 1.54 dry-volume factor already covers normal losses. Add 5% extra cement only if mixing on rough ground where spillage is likely.
Common mix ratios and uses
| Ratio | Strength class | Typical use |
|---|---|---|
| 1:1.5:3 | ≈ M300 / 4000 psi | Driveways, structural slabs |
| 1:2:4 | ≈ M200 / 3000 psi | Foundations, floors, paths |
| 1:3:6 | ≈ M100 / 1500 psi | Blinding, non-structural fill |
| 1:4 (no gravel) | M75 mortar | Bricklaying |
| 1:5 (no gravel) | M50 mortar | Plaster / render |
Common mistakes
- 1 Forgetting the 1.54 dry-volume factor and ordering a third too little material.
- 2 Using a lean 1:3:6 mix for a driveway — it will dust and crumble under vehicles.
- 3 Adding extra water to make mixing easier; every extra litre reduces final strength.
- 4 Storing cement bags directly on concrete floors, where they absorb moisture and harden.
Frequently asked questions
How many bags of cement are in 1 m³ of concrete?
For a standard 1:2:4 mix, about 6.5–7 bags of 50 kg. Richer mixes need more: 1:1.5:3 takes roughly 9 bags per cubic metre.
What does the 1.54 factor mean?
Dry cement, sand and gravel contain air voids. When mixed with water the mass compacts, so you need 1.54 m³ of dry ingredients to produce 1 m³ of cured concrete.
How much sand and gravel per bag of cement?
In a 1:2:4 mix, each 50 kg bag (0.035 m³) pairs with about 0.07 m³ of sand and 0.14 m³ of gravel — roughly 2 and 4 standard buckets respectively.
Can I use this calculator for mortar?
Yes. Choose the 1:4 or 1:5 option — these have no gravel part, so the result shows only cement bags and sand.
How long does bagged cement keep?
Use within 2–3 months of the production date. After that, strength drops noticeably; after 6 months, use it only for non-structural work.