Concrete Calculator — Cubic Yards, Cubic Metres & Bags

Enter the size of what you are pouring and this concrete calculator tells you how much to order: cubic yards or cubic metres of ready-mix, or the number of premixed bags for a small job. It handles rectangular pours such as slabs, patios, walls and footings, and round ones such as columns, piers and post holes, and adds a waste allowance to model the extra quantity you specify.

How to use this tool

1. Choose US units (feet and inches) or metric (metres and centimetres).
2. Pick the shape: a rectangle for slabs, walls and footings, or a cylinder for columns and holes.
3. Enter the dimensions and how many identical pours there are.
4. Set the waste allowance and, if you like, the ready-mix price.
5. Read the volume to order, the bag counts and the approximate weight.

Formula

Rectangle: V = L × W × T · Cylinder: V = π × (D ÷ 2)² × H · Order = V × pours × (1 + waste %)

Convert every dimension to one unit first: inches ÷ 12 gives feet and centimetres ÷ 100 gives metres. Cubic feet ÷ 27 gives cubic yards. Bag counts use the manufacturer yields of 0.30 ft³ for a 40 lb bag up to 0.60 ft³ for an 80 lb bag and are always rounded up to whole bags.

Example

A 10 × 10 ft patio poured 4 in thick is 10 × 10 × 0.333 = 33.33 ft³, or 1.23 yd³. With 10% extra that becomes 1.36 yd³ (36.67 ft³). Mixing it yourself would take 62 bags of 80 lb premix or 82 bags of 60 lb, and the wet concrete weighs roughly 5,490 lb. At $150 per yard, the ready-mix costs about $204 before any fees excluded from that unit price.