Free concrete calculator: estimate concrete volume and material quantities for slabs and footings. Input length, width, depth, and mix ratio. Get cement bags, sand, and gravel estimates.
Pouring concrete for a slab, footing, or path requires knowing exactly how much material to order — too little and your pour is incomplete, too much and you're left with hardening concrete you can't use. This calculator estimates the wet volume, applies the standard dry-volume factor, and breaks down the cement, sand, and gravel quantities based on your chosen mix ratio.
Enter the length, width, and depth of your pour. The default mix ratio is M20 (1 cement : 1.5 sand : 3 gravel), suitable for most residential slabs. Adjust the sand and gravel ratios if you need a different concrete grade. The result shows the total concrete volume, number of 50 kg cement bags, and cubic meters of sand and gravel.
Multiply length by width by depth (all in meters). Example: 5 m × 4 m × 0.1 m = 2.0 m³. The calculator multiplies by 1.54 (the dry volume factor) to account for the fact that dry ingredients compact when mixed with water — this is the standard civil engineering adjustment.
For general-purpose slabs and footings, use M20 mix (1 cement : 1.5 sand : 3 gravel). For driveways or heavy-load areas, use M25 (1 : 1 : 2). For non-structural paths and garden work, M15 (1 : 2 : 4) works well. The calculator defaults to the versatile M20 ratio.
For large slabs (>20 m²), order ready-mix concrete by the truck — it's cheaper per m³ and ensures consistent quality. For small jobs (shed base, fence posts, garden paths), mixing on-site using bags is more practical. The calculator is designed for on-site mixing estimates.