Concrete Calculator
Estimate how much concrete you need for a slab or footing. Enter the length, width and thickness to get the volume in cubic meters and cubic yards, plus the number of premix bags.
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Result
Bag yields assume ~0.0175 m³ per 40 kg bag and ~0.011 m³ per 25 kg bag — check your product's stated yield.
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Save ⟶How to use the Concrete Calculator
- 1Enter length (m) in the form on the left.
- 2Fill in the remaining fields — the result updates automatically as you type.
- 3Review the highlighted result and the supporting breakdown on the right.
- 4Use Copy, Share or Print to save or send your result.
Estimating concrete volume
Volume is simply length × width × depth in consistent units. The classic mistakes are unit mix-ups (a 10 cm slab is 0.1 m — using 10 turns a patio into a swimming pool of concrete) and forgetting waste: spillage, over-excavation and uneven subgrade typically consume an extra 5–10%.
Typical slab thicknesses: 10 cm (4") for patios and walkways, 10–15 cm (4–6") for driveways, 15 cm+ for slabs carrying vehicles or structural loads. Footings and columns are volumes too — multiply cross-section area by length and sum everything.
Bags vs. ready-mix
Below roughly 1 m³, bagged premix is practical; above that, ready-mix trucks are usually cheaper per cubic meter and far less work. One cubic meter requires around 56 forty-kilogram bags — mixing that by hand is a serious undertaking.
Order ready-mix with your waste allowance included; running short mid-pour creates a cold joint that weakens the slab.
Frequently Asked Questions
▸How many bags of concrete make 1 cubic meter?
Approximately 56 bags of 40 kg premix or about 90 bags of 25 kg premix, depending on the product yield printed on the bag.
▸How thick should a concrete slab be?
10 cm (4 inches) suits patios and walkways; driveways need 10–15 cm; anything supporting heavy vehicles should be 15 cm or more over a compacted base.
▸Why add a waste percentage?
Spillage, uneven ground and slight over-digging mean real pours consume more than the geometric volume. 5–10% extra is standard practice.