Concrete Calculator
Work out how much concrete you need for a rectangular slab or a round footing. Enter your dimensions and get the volume in cubic yards and cubic meters, plus how many 40, 50, 60, or 80 lb bags of pre-mix to buy.
You need approximately
| Bag size | Yield per bag | Bags needed |
|---|---|---|
| 40 lb | 0.30 cu ft | |
| 50 lb | 0.375 cu ft | |
| 60 lb | 0.45 cu ft | |
| 80 lb | 0.60 cu ft |
How this concrete calculator works
For a rectangular slab, volume = length × width × thickness. For a round slab or footing, volume = π × (diameter ÷ 2)² × depth. The result is converted to cubic yards (1 cubic yard = 27 cubic feet) and cubic meters.
Bag counts use the standard yields published in QUIKRETE® Concrete Mix product data: a 40 lb bag yields about 0.30 cu ft, a 50 lb bag 0.375 cu ft, a 60 lb bag 0.45 cu ft, and an 80 lb bag 0.60 cu ft. Bags are always rounded up to whole bags.
Want the math behind the bag counts? See our guide: how many bags of concrete are in a cubic yard.
Frequently asked questions
How much concrete do I need for a 10×10 slab?
A 10 ft × 10 ft slab at the standard 4-inch thickness needs about 1.23 cubic yards (33.3 cubic feet) of concrete. That is roughly 56 bags of 80 lb pre-mix, or 75 bags of 60 lb pre-mix, before any waste margin.
How many 80 lb bags of concrete make a cubic yard?
One 80 lb bag of pre-mixed concrete yields about 0.60 cubic feet, so a full cubic yard (27 cubic feet) takes about 45 bags. For 60 lb bags (0.45 cu ft each) it takes 60 bags.
Should I order ready-mix or use bags?
A common rule of thumb is that above roughly 1 cubic yard, ready-mix delivery becomes easier and often cheaper than mixing bags by hand. Below that, bagged concrete is usually the practical choice for DIY work.
How much extra concrete should I add for waste?
Most contractors add 5–10% to the calculated volume to cover spillage, uneven subgrade, and slightly over-excavated forms. This calculator adds 10% when the waste option is checked.
How thick should a concrete slab be?
Typical residential slabs are 4 inches thick for patios and walkways, and 5–6 inches where vehicles drive, such as driveways. Local codes and soil conditions can change this, so check before you pour.
Formulas last reviewed on 2026-07-02. Bag yields are based on manufacturer product data and can vary slightly by brand and mix. This tool provides planning estimates only, not engineering or construction advice — confirm quantities and slab specifications with your supplier or a licensed contractor.