Concrete Calculator

How to Use This Concrete Calculator

1. Measure the length and width of your pour in feet.
2. Enter the thickness in inches — 4 in. is standard for patios and walkways, 5–6 in. for driveways.
3. Read the result as you type: cubic yards, bag counts, weight and estimated cost. Add about 10% before you order.

Common Concrete Projects

Common Concrete Projects, With the Specs They Need

Thickness and strength are the two decisions that shape every estimate — volume scales with thickness, and stronger mixes cost a few dollars more per yard. The specs most residential projects use:

Driveways are the case worth over-building: the difference between 4 and 5 inches is roughly $1.7 per square foot of pour, and concrete driveway thickness is the single biggest factor in how long the slab survives. Run any row's dimensions through the calculators above to get its yards and cost.

What Strength (PSI) Do You Need?

The psi number on a concrete quote (3,000 psi, 4,000 psi…) is the compressive strength the mix reaches at 28 days. Higher psi means more cement in the drum — typically another $5–$10 per cubic yard per step — and it matters most where loads concentrate or water freezes.

How to choose when you're torn: match the heaviest thing that will ever park on the slab, not today's use. A 3,500 psi mix covers most patios, walkways and shed pads; 4,000 psi is the residential standard for driveways and garage floors; 4,500 psi and up is for structural slabs and commercial work — and for those, the spec usually comes from an engineer anyway. In freeze-thaw climates, ask for air-entrained concrete at whatever strength you choose: tiny entrained bubbles give freezing water somewhere to expand, which is what keeps outdoor slabs from spalling apart in a few winters.

Bagged Mix or Ready-Mix: How to Decide

Concrete is sold two ways — sacks you mix yourself, or a truck that pours — and the right answer is almost entirely about volume:

The arithmetic behind the table: a cubic yard takes 45 of the 80-lb bags — a full day of mixing for two people — and bagged mix works out to roughly twice the per-yard price of delivered concrete. Bags win where a truck can't go or a short-load fee would dwarf the pour. Price both routes for your exact dimensions with the concrete cost calculator, and the bags-per-yard guide has the counts worked out per project.

What Is a Concrete Estimator?

A concrete estimator is any tool that predicts how much concrete a job needs before you buy it. This calculator estimates four things at once: volume in cubic yards, the number of 40, 60 or 80-lb bags that equals, the weight of the wet concrete, and what it should cost. It is the same math a contractor runs before calling the batch plant — you just see the answer on the spot instead of in an invoice.

Because the estimate updates as you type, you can compare scenarios in seconds: a 4-inch slab against a 6-inch one, bagged mix against ready-mix delivery, a slightly smaller footprint. Run the numbers before you order and you will never pay for a yard of concrete you don't need.

How Much Concrete Do I Need?

The quick answer: volume (ft³) = length (ft) × width (ft) × thickness (ft), then divide by 27 to get cubic yards. Thickness is usually measured in inches, so divide it by 12 first.

Example: a 12 × 20 ft patio at 4 inches thick is 12 × 20 × 0.333 = 80 ft³, which is 80 ÷ 27 ≈ 2.96 cubic yards — order about 3.3 yards with the 10% allowance. The calculators on this site run this math for every common project shape; for flat pours, concrete slab calculator does it in one step.

Frequently Asked Questions