Concrete Volume Calculator
Calculate concrete volume and the number of bags needed for a slab, footing, or small pour.
How this calculator works
Volume = length × width × thickness, with thickness converted to the same unit first. Bags needed = volume ÷ yield per bag, rounded up. Always add 5–10% extra for spillage and an uneven subgrade.
Length and width are entered in feet or meters; thickness uses a smaller unit (inches or centimeters) since slabs are typically just a few inches deep. Bag yield is based on standard 40/60/80 lb bags (imperial) or 25 kg bags (metric).
All calculations run in your browser only — nothing you type is sent to a server. Results are estimates for planning purposes; always round up and buy a small surplus for cuts, waste, and future repairs.
Example calculations
10 × 10 ft slab, 4 in thick, 60 lb bags
≈ 1.23 yd³ (0.94 m³) → ≈ 74 bags.
3 × 2 m footing, 30 cm thick
≈ 1.8 m³ → ≈ 155 bags (25 kg).
Frequently asked questions
How much extra concrete should I order beyond the calculated volume?
Add 5–10% on top of the calculated volume to account for an uneven subgrade, spillage, and minor form variations — running short mid-pour is a much bigger problem than having a little extra.
Is bagged concrete practical for a large slab?
For anything beyond a small pour (a few cubic yards), ready-mix delivered by truck is usually more practical and often cheaper per yard than dozens of bags — use this calculator's volume figure to get a delivery quote.
Does slab thickness really need to be exact?
Thickness has an outsized effect on volume since it's multiplied by the full length and width — even a half-inch difference can meaningfully change how many bags you need, so measure it carefully at a few points.