Concrete Calculator

Calculate how much concrete you need for a slab, patio, footing, or column. Get results in cubic yards for ready-mix and 40, 60, or 80 lb bags.

Mason ReidFounder and Lead Estimator at MeasureThen

Last updated 2026-08-21

What Is a Concrete Calculator?

A concrete calculator tells you exactly how much concrete you need for a slab, patio, footing, or column by turning your length, width, and thickness into cubic yards. It also converts that volume into ready-mix yards and 40, 60, or 80 lb bags so you can order the right amount the first time. Built for homeowners and DIYers, it removes the guesswork before you call a supplier or head to the home center.

How It Works

Volume (ft³) = Length × Width × (Thickness ÷ 12). Convert to cubic yards by dividing by 27.

Example

For a 10 ft × 10 ft pad at 4 in thick with 10% waste: 10 × 10 × (4 ÷ 12) = 33.3 ft³, × 1.1 = 36.7 ft³ ≈ 1.36 cubic yards (62 × 80 lb bags).

How to Calculate

Measure the length and width of your pour in feet and the thickness in inches. For a 10 ft by 10 ft patio pad, that is 10 and 10 with a 4 in thickness.
Enter a waste factor of 5 to 10% to cover spillage, uneven ground, and formwork. Use 10% for a typical pad.
The calculator computes the volume: 10 × 10 × (4 ÷ 12) = 33.3 cubic feet, then × 1.1 for waste = 36.7 cubic feet.
Read the result in cubic yards by dividing by 27, which gives about 1.36 cubic yards for this example.
Use the bag conversion to see you need about 62 of the 80 lb bags, or order ready-mix for the 1.36 yard pour.

Bags of Concrete per Cubic Yard by Bag Size

Bag Size	Yield per Bag	Bags per Cubic Yard
40 lb	0.30 cu ft	90 bags
60 lb	0.45 cu ft	60 bags
80 lb	0.60 cu ft	45 bags
Ready-mix	27 cu ft per yard	1 yard minimum

Sources

Frequently Asked Questions

What waste factor should I use?

A 5–10% waste factor is typical for slabs. Add more (10–15%) for footings or columns where forms and rebar cause extra waste.

How many bags are in a cubic yard?

Roughly 45 × 80 lb bags, 60 × 60 lb bags, or 90 × 40 lb bags fill one cubic yard.

Is concrete ordered by the cubic yard?

Yes. Ready-mix suppliers deliver by the cubic yard, so divide your volume in cubic feet by 27.

Mason ReidFounder and Lead Estimator at MeasureThen

Mason Reid founded MeasureThen after two decades of hands-on work in construction and estimating. Across residential and light commercial projects, he sized concrete pours, framed walls, hung drywall, and priced out roofing, fencing, and deck work — learning the exact math that every job depends on. At MeasureThen he writes the formulas, checks every calculator against real-world assumptions, and makes sure each one is simple enough for a homeowner to trust and a contractor to use. When he is not measuring twice, he is helping projects stay on budget.

Every MeasureThen calculator uses simple, transparent formulas and standard industry assumptions drawn from common construction practice. We show the math behind each result and include worked examples so you can follow along and double-check the numbers. Results are estimates: materials, labor, and pricing vary by region and market, so always confirm important figures with a licensed professional and your local building codes.