Concrete Calculator
Volume of concrete plus the cement, sand and gravel to mix it.
| Concrete grade | M300 |
|---|---|
| Cement | 2,006 kg |
| Sand | 3,485 kg |
| Gravel | 6,230 kg |
| Water | 977 l |
How it works
Concrete volume is the plain geometry of what you are pouring — length times width times thickness, times the number of identical elements. The quantities that follow come from standard mix ratios per cubic metre of finished concrete, not per cubic metre of loose ingredients.
Order a little more than the arithmetic says. Concrete cannot be topped up once it has started setting, the ground under a footing is never perfectly level, and a partial second delivery costs far more than the extra you would have poured. Ten percent is the usual allowance for a slab, more for uneven ground.
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How the Concrete Calculator works
A concrete calculator works out the volume of a pour and the cement, sand, gravel and water needed to make it. It handles slabs, strip footings and columns — enter the dimensions and the number of identical elements.
How the volume is calculated
Volume is length times width times thickness. For a slab those are its dimensions. For a strip footing, enter the total run of the strip along with its width and height. For columns, enter the section and height of one and set the count separately.
The cubic metres refer to finished concrete, not to the sum of the loose ingredients. This matters: gravel, sand and cement take up less space mixed than separately, because the fine fractions fill the voids between the coarse ones. Adding up component volumes is a common mistake that over-orders by around thirty percent.
Grades and mix ratios
The grade is compressive strength. M200 suits screeds, paths and light bases. M250 and M300 are the working grades for domestic strip footings and slabs. M400 is for serious loads and is normally ordered ready-mixed rather than batched on site.
The higher the grade, the more cement and the less sand per cubic metre. The ratio shown here is by weight rather than by bucket, which is the more accurate basis — the bulk density of sand varies a great deal with moisture content.
How much to order above the calculation
Always more than the arithmetic says. Concrete cannot be topped up once it starts setting, the ground under a footing is never perfectly level, and a partial second delivery costs far more than the extra you would have poured. Ten percent is usual over a prepared base, up to fifteen on uneven ground.
Once the slab is poured it is worth working out the screed that goes on top of it, and the brick for the walls if they come next.
FAQ
How much cement is in a cubic metre of concrete?expand_more
About 280 kg for M200, 330 kg for M250, 380 kg for M300 and 450 kg for M400. In 50 kg bags that is roughly 6, 7, 8 and 9 bags respectively per cubic metre of finished mix.
What grade do I need for a strip footing?expand_more
M250 to M300 for a typical house. M200 is acceptable for light structures and outbuildings; M400 is overkill and more expensive. The specific grade should come from the design, based on loads and ground conditions.
Can I mix concrete by hand?expand_more
For small volumes up to a cubic metre, yes, with a mixer. A foundation slab is better poured ready-mixed in one go: batching on site inevitably leaves gaps between loads, and the monolith becomes layers with cold joints.