Cement Bag Calculator

Cement Bag Calculator

Find out how many bags of cement you need for a concrete pour, together with the sand, coarse aggregate (gravel) and water. Enter the concrete volume, choose a mix ratio and bag size, and the calculator does the rest using the standard dry-volume method.

Nominal mix ratiosSand, aggregate & waterMetric & imperialLast updated: November 2, 2026

Calculate cement bags

m³
Wet (finished) volume of concrete
%
For spillage and bulking

How cement is calculated: the dry-volume method

When cement, sand and aggregate are mixed with water, the fine particles fill the gaps between the stones and the mix shrinks. To make 1 m³ of finished concrete you need about 1.54 m³ of loose dry ingredients. That dry volume is then split by the mix ratio.

1. Dry volume

Vdry = Vwet × 1.54 × (1 + extra%)

Some engineers use 1.52 or 1.57; 1.54 is the most widely used factor.

2. Cement

Cement (kg) = Vdry × c ÷ (c + s + a) × 1,440

1,440 kg/m³ is the bulk density of cement. Divide by the bag weight and round up.

3. Sand and aggregate

Sand = Vdry × s ÷ (c+s+a)  ·  Aggregate = Vdry × a ÷ (c+s+a)

Approximate weights use 1,600 kg/m³ for dry sand and 1,500 kg/m³ for 20 mm aggregate.

4. Water

Water (litres) = cement (kg) × w/c ratio

A water–cement ratio of 0.45–0.55 suits most hand and mixer work. The calculator uses 0.5.

Worked example: 1 m³ of M15 (1 : 2 : 4)

  1. Dry volume = 1 × 1.54 = 1.54 m³ (no extra allowance)
  2. Sum of ratio = 1 + 2 + 4 = 7
  3. Cement = 1.54 × 1/7 × 1,440 = 316.8 kg → 6.34 → 7 × 50 kg bags
  4. Sand = 1.54 × 2/7 = 0.44 m³; Aggregate = 1.54 × 4/7 = 0.88 m³
  5. Water = 316.8 × 0.5 ≈ 158 litres

Cement, sand and aggregate per cubic metre

Mix (grade)Cement50 kg bagsSandAggregate
1 : 1 : 2 (M25)554 kg11.10.385 m³0.770 m³
1 : 1.5 : 3 (M20)403 kg8.10.420 m³0.840 m³
1 : 2 : 4 (M15)317 kg6.30.440 m³0.880 m³
1 : 3 : 6 (M10)222 kg4.40.462 m³0.924 m³
1 : 4 : 8 (M7.5)171 kg3.40.474 m³0.948 m³

Values are for 1 m³ of finished concrete with no allowance. For one cubic yard, multiply by 0.765. A 94 lb US bag holds 42.6 kg, so 1 m³ of 1 : 2 : 4 needs about 7.4 of those bags.

Nominal vs design mix: ratios like 1 : 2 : 4 are nominal mixes for small and medium works. Large or high-strength jobs (M25 and above) normally use a design mix tested by a lab or supplied as ready-mix.

How to use the calculator

  1. Get your volume. Use the slab, footing or volume calculator first if you don’t know it.
  2. Choose the mix that suits the job and the bag size sold near you.
  3. Add an extra allowance of about 5% for spillage and sand bulking.
  4. Calculate and buy the rounded-up number of bags.

Frequently asked questions

How many bags of cement are in 1 cubic metre of concrete?

About 6.3 bags of 50 kg for a 1:2:4 (M15) mix, 8.1 bags for 1:1.5:3 (M20) and 4.4 bags for 1:3:6 (M10), using the dry-volume method.

Why multiply by 1.54?

Dry ingredients pack together when water is added, so the finished concrete occupies about 35% less volume than the loose materials. Multiplying by 1.54 accounts for those voids.

How much water do I need per bag of cement?

At a water–cement ratio of 0.5, a 50 kg bag needs about 25 litres of water, and a 94 lb bag about 5.6 US gallons. Use less water for stronger concrete.

How many bags of cement per cubic yard?

For a 1:2:4 mix, about 242 kg per cubic yard, which is roughly 5.7 bags of 94 lb or 4.8 bags of 50 kg.

Concrete Slab CalculatorVolume for floors and patios Mortar Mix CalculatorCement and sand for mortar Sand CalculatorSand by volume and weight Gravel CalculatorAggregate tonnage

Results are estimates using the nominal-mix dry-volume method. Actual quantities vary with aggregate grading, moisture and compaction.

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