Concrete Calculator
Work out how much concrete you need for a slab, patio, shed base or footing — in cubic yards, cubic metres and pre-mix bags.
4 in / 10 cm is typical for a patio or shed base
Your result
Cubic yards
1.36 yd³
Cubic metres
1.04 m³
Cubic feet
36.7 ft³
80 lb bags (0.60 ft³ each)
62 bags
60 lb bags (0.45 ft³ each)
82 bags
25 kg bags (≈0.011 m³ each)
95 bags
How concrete volume is calculated
Concrete is ordered by volume. Multiply length × width × thickness, keeping every measurement in the same unit, and you have the volume of the slab. In the US that number is usually converted to cubic yards (27 cubic feet per yard); in the UK and Europe it stays in cubic metres.
Always add a margin. Ground is rarely perfectly level, forms bow slightly and some concrete is lost in the mixer or barrow. 5–10% is normal for a slab, more for an uneven sub-base.
Bags or ready-mix?
Pre-mixed bags are practical up to roughly 1 yd³ (0.75 m³). Beyond that, a ready-mix truck is usually cheaper and gives a more consistent pour. Bag yields above are typical manufacturer figures — check the bag you buy, as yields vary by brand.
Frequently asked questions
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