Concrete calculator
Work out concrete volume for slabs, columns, beams and footings in m³, ft³ or yd³, plus cement, sand, gravel and water from C25 or C30 reference mixes, with an optional wastage allowance.
Runs in your browserEvery computation happens in your browser — your data never leaves this device.
Element and mix
Slab = length × width × thickness, column = section area × height, beam = length × width × height, footing = length × width × thickness. The mixes are common reference ratios — always follow the design mix on site.
Quantities
2.000 m³
2.000 m³
2.100 m³
74.16 ft³
2.75 yd³
714.0 kg · 15 bags × 50 kg
999.6 kg
1999.2 kg
321.3 L
3712.8 kg
What this tool does
- Order the right amount of ready-mix for a slab or a beam instead of coming up half a cubic meter short.
- Convert a volume into cement, sand, gravel and water for site mixing, including the number of 50 kg cement bags.
- Compare C25 with C30: at the same volume C30 needs roughly 18% more cement, which makes the price difference easy to judge.
- Get cubic yards and cubic feet to check a quote or a drawing that uses imperial units.
Example
Input
Slab 5 × 4 × 0.1 m, C25, 5% wastage
Output
Volume per element 2.000 m³, net volume 2.000 m³, order volume 2.100 m³ (74.16 ft³ / 2.75 yd³), cement 714.0 kg (15 bags × 50 kg), sand 999.6 kg, gravel 1999.2 kg, water 321.3 L, total dry mass 3712.8 kg
The mix is the reference weight ratio 1:1.4:2.8:0.45 (340 kg cement per m³). It is a common site reference, so follow the design mix for actual work.
Frequently asked questions
Is the volume net or does it include wastage?
Both are shown. The net volume is the geometric volume; the order volume is that figure increased by the wastage you entered, and the materials are based on it, so pumping losses, spillage and uneven formwork are already covered.
What wastage figure should I use?
3–5% is typical for ready-mix placement; use 5–10% for site mixing, pumping or awkward shapes. The tool caps it at 30% because a larger figure usually means the dimensions or the method need a second look.
Why is a round column π/4 × diameter²?
The area of a circle is π × radius², which equals π/4 × diameter² — engineers normally work straight from the diameter. With double-precision π, a 0.4 m diameter column 3 m tall comes to about 0.377 m³ each.
Why are the cement bags rounded up?
Cement is sold in 50 kg bags, so 714 kg means 15 bags (14.28 rounded up). Sand and gravel are usually bought by weight or volume and can be rounded to the nearest convenient figure — a little extra beats a mid-pour shortage.
Where do the C25 and C30 mixes come from?
They are reference magnitudes for common site mixes by weight (C25 = 1:1.4:2.8:0.45 with 340 kg cement per m³; C30 = 1:1.2:2.5:0.42 with 400 kg per m³). They are good enough for estimating and comparing prices, but real work must follow the design mix and laboratory trial mix.
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