Concrete Calculator

What this means

Concrete volume is simply length × width × thickness. The tricky part is units — thickness is usually given in centimetres or inches while the slab is in metres or feet, so it must be converted before multiplying. We add waste for spillage and uneven sub-base, then estimate pre-mix bags from a standard yield per bag.

Recommendations

• •For anything above roughly 1 m³ (about 1.3 yd³), ready-mix delivery is usually cheaper and easier than mixing bags by hand.
• •Order 5–10% extra — you can't pause a pour to fetch more, and a short load means a cold joint.
• •A compacted, level sub-base prevents thickness creep that quietly increases the volume you need.

Watch out

• •Bag yields vary by product and mix consistency — treat the bag count as an estimate and check the packaging.
• •Footings and reinforced slabs may need specific mixes and depths — follow your structural drawings or local code.