Concrete Volume and Material Calculator (Cement, Sand, Aggregate)
How the formula works
Concrete is a mix of cement, sand (fine aggregate), coarse aggregate and water. To order the right amount of materials, you first find the volume of concrete for your element (slab, beam, footing, wall or column), and then split that volume into cement, sand and aggregate using the mix ratio. This calculator does all of this and also gives the water needed.
Step 1: Concrete volume
Rectangular element: Volume = Length × Width × Height (or thickness) × Number of elements
Circular element: Volume = π ÷ 4 × Diameter² × Height × Number of elements
Step 2: Dry volume of materials
Volume with wastage = Volume × (1 + Wastage %)
Dry volume = Volume with wastage × 1.54
The dry volume is larger than the wet volume because the loose materials shrink when they are mixed with water and compacted. The factor 1.54 is the commonly used value.
Step 3: Split by the mix ratio
Cement volume = Dry volume × C ÷ (C + S + A)
Sand volume = Dry volume × S ÷ (C + S + A)
Aggregate volume = Dry volume × A ÷ (C + S + A)
Step 4: Convert to bags, weight and water
Cement (kg) = Cement volume × 1,440
Number of bags = Cement (kg) ÷ Bag size (kg)
Sand (kg) = Sand volume × 1,600
Aggregate (kg) = Aggregate volume × 1,500
Water (litres) = Cement (kg) × Water cement ratio
Where
- C : S : A = the mix ratio of cement : sand : aggregate, such as 1 : 1.5 : 3 for M20
- 1,440 kg/m³ = bulk density of cement
- 1,600 kg/m³ = bulk density of sand
- 1,500 kg/m³ = bulk density of coarse aggregate
Common nominal mixes
- M5 (1 : 5 : 10): lean concrete, filling
- M7.5 (1 : 4 : 8): lean concrete under foundations
- M10 (1 : 3 : 6): plain concrete, bedding
- M15 (1 : 2 : 4): plain concrete and light work
- M20 (1 : 1.5 : 3): common for slabs, beams and columns in small buildings
- M25 (1 : 1 : 2): for structural work with higher strength needs
Higher grades and larger structures are usually made by a design mix and not by a nominal mix. Follow your structural engineer and the code that applies to your project.
How to use the calculator
- Select the shape. For a slab, enter the length, the width and the thickness. For a wall, enter the length, the thickness and the height. For a beam, enter the length, the width and the depth.
- Enter the number of elements, select the unit, then select the mix, the wastage, the water cement ratio and the bag size.
- If you already know the volume, select the known volume option and enter it.
- Click Calculate. You can then download the result as a PDF.
Important notes
- The result is an estimate. The densities and the 1.54 factor change with the materials and the moisture.
- Cement bags are rounded up to the next whole bag.
- Add the allowance that your site practice needs, such as spillage and waste, in the wastage option.
Worked example
Example 1: Slab with M20 concrete
A slab is 5 m long, 4 m wide and 0.15 m thick. Use M20 (1 : 1.5 : 3), wastage of 5 %, water cement ratio of 0.50 and 50 kg bags.
Step 1: Volume
5 × 4 × 0.15 = 3.00 m³ (105.94 ft³)
Step 2: Wastage and dry volume
Volume with wastage = 3.00 × 1.05 = 3.15 m³
Dry volume = 3.15 × 1.54 = 4.85 m³
Step 3: Split by 1 : 1.5 : 3 (total 5.5 parts)
Cement = 4.85 × 1 ÷ 5.5 = 0.882 m³
Sand = 4.85 × 1.5 ÷ 5.5 = 1.32 m³
Aggregate = 4.85 × 3 ÷ 5.5 = 2.65 m³
Step 4: Bags, weight and water
Cement = 0.882 × 1,440 = 1,270 kg = 25.4 bags, so order 26 bags of 50 kg
Sand = 1.32 m³ = 2.12 tonnes
Aggregate = 2.65 m³ = 3.97 tonnes
Water = 1,270 × 0.50 = 635 litres
Example 2: Six round columns with M15
Six circular columns, each 0.4 m in diameter and 3 m high. Use M15 (1 : 2 : 4) with 5 % wastage.
Volume = π ÷ 4 × 0.4² × 3 × 6 = 2.26 m³
Dry volume = 2.26 × 1.05 × 1.54 = 3.66 m³
Cement = 3.66 × 1 ÷ 7 = 0.522 m³ = 752 kg, so 16 bags of 50 kg
Sand = 1.05 m³ (1.67 tonnes), aggregate = 2.09 m³ (3.14 tonnes), water = 376 litres
Example 3: Known volume
You know that you need 10 m³ of concrete. Use M15 (1 : 2 : 4) with 5 % wastage.
Volume with wastage = 10.50 m³, dry volume = 16.17 m³
Cement = 3,326 kg, so 67 bags of 50 kg
Sand = 4.62 m³ (7.39 tonnes), aggregate = 9.24 m³ (13.86 tonnes), water = 1,663 litres
Example 4: Slab in feet
A slab is 10 ft × 10 ft and 6 inches (0.5 ft) thick. Use M25 (1 : 1 : 2), no wastage, water cement ratio of 0.45 and 50 kg bags.
Volume = 10 × 10 × 0.5 = 50 ft³ = 1.42 m³ (1.85 yd³)
Dry volume = 1.42 × 1.54 = 2.18 m³
Cement = 2.18 × 1 ÷ 4 = 0.545 m³ = 785 kg, so 16 bags of 50 kg
Sand = 0.55 m³ (0.87 tonnes), aggregate = 1.09 m³ (1.64 tonnes), water = 353 litres
Common mistakes
- Using the wet volume as the dry volume. The dry volume of materials is about 1.54 times the volume of concrete. If you skip this factor, you will order too little.
- Mixing units. Enter all the dimensions in the same unit. A slab thickness of 150 mm is 0.15 m, not 15 m.
- Forgetting the number of elements. For many footings or columns, enter the count so that the total volume is right.
- Not allowing for wastage. Spillage, uneven formwork and leftover concrete can use 3 to 10 % extra. Select a wastage allowance.
- Counting the cement by volume of bags. A 50 kg bag is about 0.0347 m³, so use the weight in kg to find the bags.
- Using a nominal mix for structural design. Higher grades are normally design mixes with a tested water cement ratio and admixtures. Follow the structural drawings.
- Using too much water. A higher water cement ratio makes the concrete workable, but it lowers the strength and the durability.
- Ignoring the moisture in sand. Wet sand bulks up. The real volume of sand you need on site may be higher than the dry value.
- Forgetting deductions and extras. Openings, steel, haunches and rounded corners change the real volume a little. Add or deduct them if the accuracy matters.
Frequently asked questions
How do I calculate the volume of concrete?
For a rectangular element multiply the length, the width and the height (or thickness). For a slab of 5 m × 4 m × 0.15 m, the volume is 3 m³. For a round column use π ÷ 4 × diameter² × height.
How do I calculate the cement, sand and aggregate for concrete?
Find the volume, multiply it by 1.54 to get the dry volume, and split it by the mix ratio. For 1 : 1.5 : 3, the cement is 1 part out of 5.5 parts, the sand is 1.5 parts and the aggregate is 3 parts.
Why is the factor 1.54 used?
The loose dry materials take more space than the finished concrete, because the sand fills the gaps in the aggregate and the cement fills the gaps in the sand. The factor 1.54 is the common allowance for this.
How many bags of cement are needed for 1 m³ of concrete?
It depends on the mix. For 50 kg bags, M20 (1 : 1.5 : 3) needs about 8 bags, M15 (1 : 2 : 4) needs about 6.3 bags and M25 (1 : 1 : 2) needs about 11 bags per m³.
What does M20 mean?
M stands for mix and 20 is the characteristic compressive strength in N/mm² after 28 days. The nominal ratio of M20 is 1 : 1.5 : 3 (cement : sand : aggregate).
How much water is needed for concrete?
The water is the cement weight multiplied by the water cement ratio. For 1,270 kg of cement at a ratio of 0.50, the water is 635 litres. Add or reduce water on site for the moisture in the aggregate.
How much wastage should I add?
A wastage of 3 to 5 % is typical for a well managed site. Use a higher value for small or complex pours.
How do I convert cubic feet and cubic yards to cubic metres?
1 m³ is 35.31 ft³ and 1.308 yd³. The calculator shows the volume in all three units.
Can I use this for a slab, a beam, a footing, a wall and a column?
Yes. Use the rectangular option for all of them and enter the right dimensions. Use the circular option for round columns and piles.
Does this replace the structural design?
No. It only gives the quantities for a chosen volume and mix. The grade, the mix design and the sizes must come from the structural design and the code.