Concrete Calculator

Pick the pour shape — slab, footing, rectangular column, or round tube — enter its dimensions, and get the volume in cubic yards with a waste factor applied. It also converts the volume into 40, 60, and 80-lb premixed bag counts using the standard published yields (0.011, 0.017, and 0.022 yd³ per bag), all editable.

Common uses

• Order ready-mix for a patio slab without over- or under-shooting
• Count 80-lb bags for a handful of fence-post footings
• Size a sonotube pour for deck piers

Example

Slab 10 × 10 ft, 4 in thick, 10% waste

1.23 yd³ exact → order 1.36 yd³ or 62 × 80-lb bags

Limitations

• Bag yields are typical label values; brands vary slightly
• No allowance for uneven subgrade beyond the waste factor

How much concrete do I need for a 10x10 slab?

At the common 4 in thickness, a 10×10 ft slab is 1.23 cubic yards of concrete exactly, or about 1.36 yd³ with a 10% waste factor. That's roughly 62 80-lb bags — enough that ordering ready-mix is usually worth considering.

How many 80-lb bags of concrete make a cubic yard?

About 45. An 80-lb bag of premixed concrete yields roughly 0.022 cubic yards (0.6 cu ft), so a full yard takes 45–46 bags; 60-lb bags run about 60 per yard and 40-lb bags about 90.

Why should I add a waste factor to a concrete order?

Because coming up short mid-pour is far worse than having a little extra — you can't cleanly add fresh concrete to a pour that has started to set. A 5–10% cushion covers spillage, uneven subgrade, and forms that hold slightly more than measured.

How do I calculate concrete for a round sonotube pier?

Use the cylinder formula: π × radius² × height. This calculator's tube mode does it for you from the tube diameter in inches and height in feet, and multiplies by the number of identical piers.

Is anything uploaded when I calculate a concrete pour?

No. The volume and bag math runs entirely in your browser — your project dimensions never leave your device and nothing is stored on a server.