Concrete Calculator

Estimate how much concrete you need for a slab, patio, footing, or round column. Get cubic yards, cubic feet, and 40, 60, and 80 lb bag counts with a waste allowance. Everything runs in the browser.

Cubic yards
Bags needed
Stays on your device

Concrete volume is length × width × thickness. Convert thickness from inches to feet, multiply, and divide cubic feet by 27 to get cubic yards. For round columns and post holes the calculator uses π × radius² × height.

Example: a 10 ft × 10 ft patio poured 4 inches thick is 33.3 cubic feet, or 1.23 cubic yards. With 10% waste that is about 1.36 cubic yards, or 62 bags of 80 lb premix.

Browse the Household hub, or open the roofing calculator, house sq-ft estimator, and cubic yard calculator.

How to use the concrete calculator

Choose a slab, patio, or footing, or a round column.
Enter length, width, and thickness, or diameter and height.
Set the quantity if you are pouring several identical pieces.
Adjust the waste allowance (10% by default).
Read cubic yards for ready-mix or the bag count for premix.

Frequently asked questions

What is a concrete calculator?

A concrete calculator estimates how much concrete you need for a slab, patio, driveway, footing, or round column. It returns the volume in cubic yards and cubic feet and the number of premix bags.

How do I calculate cubic yards of concrete?

Multiply length in feet by width in feet by thickness in feet, then divide by 27. A 10 ft by 10 ft slab 4 inches thick is 10 × 10 × 0.333 = 33.3 cubic feet, or about 1.23 cubic yards.

How many 80 lb bags of concrete do I need?

An 80 lb bag yields about 0.60 cubic feet. Divide the cubic feet by 0.60 and round up. A 10 ft by 10 ft by 4 in slab needs about 56 bags before waste, or 62 with 10% waste.

How thick should a concrete slab be?

Four inches is common for patios, sidewalks, and shed floors. Driveways and garage floors are often 5 to 6 inches. Check local code and your contractor for loads and soil conditions.

How much extra concrete should I order?

Most people add 5% to 10% for spillage, uneven grade, and form bulge. The calculator defaults to 10% waste, and you can change it to 0 to see the exact volume.

How do I calculate concrete for a round column or post hole?

Volume is π × radius² × height. A 12 inch diameter hole 4 feet deep holds about 3.14 cubic feet, or 0.12 cubic yards. Enter the quantity to total several holes at once.

Should I use bags or ready-mix?

Bags work well for small jobs under about one cubic yard. For larger slabs and driveways, ready-mix delivered by the cubic yard is usually easier and more consistent.

Is my information saved or uploaded?

No. The concrete calculator runs entirely in your browser. Measurements are not sent to a server or stored, and there is no account.