Concrete Calculator
Work out how much concrete you need for a slab, footing or pad.
About this calculator
Ordering too little concrete means a cold joint and a costly delay. Ordering too much wastes money and leaves you with a disposal problem. This calculator gives you the exact volume you need for a slab, footing, pad or path, plus a bag count if you’re mixing on site.
How it works
Volume is simply length × width × thickness. Use consistent units (the calculator uses metres for all three) and the result is a true cubic-metre figure.
Cubic yards are the standard ordering unit in North America: 1 m³ is about 1.308 yd³. The calculator shows both so you can compare quotes regardless of where your supplier is.
If you’re mixing on site, a standard 25 kg pre-mix bag yields roughly 0.011 m³ of cured concrete. The calculator rounds the bag count up — you always want a few spare bags rather than running short mid-pour.
For most jobs add 5–10% on top of the calculated volume to allow for slight variation in slab depth, formwork bulge and waste. For a critical pour with no contingency, talk to your supplier about safety margins.
Formula
volume (m³) = length × width × thickness (all in metres)
volume (yd³) = volume (m³) × 1.30795
bags (25 kg) = ceil( volume (m³) / 0.011 )Examples
Garden slab: 5 × 4 × 0.1 m
A 5×4-m slab 10 cm thick needs 2 m³ of concrete. Mixing on site would require about 182 standard pre-mix bags.
Result: 2.0 m³ — 2.62 yd³ — 182 bags of 25 kg
Pathway: 10 × 1.2 × 0.08 m
A 10-m path, 1.2 m wide and 8 cm thick, takes just under a cubic metre of concrete.
Result: 0.96 m³ — 1.26 yd³ — 88 bags