Concrete Calculator
Find the volume of concrete for a slab, footing or column in m³, ft³ and yd³, with bags if you want them.
How it works
Choose slab, footing, column or custom, enter the dimensions and the number of identical pieces, and set the waste allowance. Length and width share one unit, and the depth has its own. Optionally enter the bag yield from the label to get a bag count.
box volume = length × width × depth
round column = π × (diameter ÷ 2)² × height
volume to order = volume × pieces × (1 + waste ÷ 100)
bags = ceil(volume to order ÷ bag yield)Example
A slab 5 m × 4 m and 100 mm thick is 5 × 4 × 0.1 = 2 m³. With 5% waste that is 2.1 m³, which is 74.16 ft³ or 2.75 yd³. If the bag label says one bag makes 0.6 ft³, then 74.16 ÷ 0.6 = 123.6, so 124 bags.
Common mistakes
- Mixing depth units. A 100 mm slab typed as 100 in the metre field is 100 m deep. Each unit selector applies only to its own fields.
- Using another brand's bag yield. Yields differ by brand and bag size, so read the label of the bag you will buy.
- Treating the result as a recipe. It is the volume of finished concrete, not a quantity of cement, sand and gravel.
About this calculator
Pick a shape, enter its length, width and depth in the units you measured in, and say how many identical pieces there are. The calculator gives the volume of one piece, the total, and the volume to order after a waste allowance, in cubic metres, cubic feet and cubic yards. Round columns use their diameter and height.
This is the volume of wet concrete, not a mix design: it does not give cement, sand or aggregate amounts. A bag count appears only when you enter how much concrete one bag makes, because that yield differs by brand and bag size. Check the bag label. Reinforcement, formwork and compaction loss are not modelled.
Frequently asked questions
How do I calculate the volume of concrete?
Multiply length by width by depth, all in the same unit. A 5 m × 4 m slab 0.1 m thick is 2 m³. For a round column use π × (diameter ÷ 2)² × height, then multiply by the number of columns.
Does it tell me how much cement, sand and gravel to buy?
No. It gives the volume of concrete only. Mix proportions depend on the strength you need and on local practice, so use the mix on the supplier's or bag's instructions.
How many bags will I need?
Enter the volume one bag makes, from its label, in m³ or ft³. Bags are the volume to order divided by that yield, rounded up. With no yield entered there is no bag count, because there is no single yield that fits every bag.
Why is there a waste allowance?
Spillage, uneven ground and over-excavation use more concrete than the box volume. The 5% default is an example value and you can change it from 0 to 100.
How do cubic metres convert to cubic yards?
One cubic yard is 0.7646 cubic metres, so 1 m³ is about 1.308 yd³. One cubic metre is about 35.31 cubic feet. All three are shown together.