How much concrete do I need for a slab?

Multiply length by width by the thickness in feet for cubic feet, then divide by 27 for cubic yards. A 10 by 10 foot slab 4 inches thick is about 33 cubic feet, or 1.23 cubic yards before waste, roughly 1.4 cubic yards with a 10 percent allowance.

How many bags of concrete are in a cubic yard?

A cubic yard is 27 cubic feet. An 80 pound bag yields about 0.6 cubic feet, so a cubic yard takes about 45 bags. A 60 pound bag yields about 0.45 cubic feet, so a cubic yard takes about 60 bags.

Should I use bags or ready mix concrete?

Mixing bags by hand is practical up to roughly half a cubic yard. Above that, ordering ready mix delivered by truck is usually cheaper and far less work. Most ready mix suppliers have a short load minimum, often around one cubic yard.

How much does a cubic yard of concrete cost?

Ready mix concrete runs roughly 120 to 170 dollars per cubic yard delivered in 2026, before short load fees, with the national average near 140. Bagged concrete works out more expensive per yard but avoids delivery for small jobs.

Home / Concrete Calculator

Concrete Calculator

A concrete calculator tells you how much concrete a slab, footing, or patio needs. It takes the length, width, and thickness, and returns the volume in cubic yards and cubic feet, the number of 60 and 80 pound bags, and the cost. Pick a project below or type your own dimensions. Everything runs in your browser, with no signup.

Updated for 2026

Your pour

Pick a project or type the dimensions. Results update instantly.

Project preset

Length

Width

Thickness

inches

Ready mix price

$/ yd³

Concrete to order

Volume

0 ft³

Exact cubic yards

0 yd³

80 lb bags

60 lb bags

Ready mix cost (with 10% waste)

Concrete for common projects

Cubic yards needed (before waste) at 4 inches thick. Tap any row to load it into the calculator.

Project	Size	Volume	Cubic yards

How the concrete volume is calculated

Concrete is ordered by volume. Multiply length by width by thickness, with the thickness converted from inches to feet, then divide by 27 to get cubic yards:

Cubic yards = Length × Width × ( Thickness ÷ 12 ) ÷ 27

There are 27 cubic feet in a cubic yard. An 80 pound bag of concrete mix yields about 0.6 cubic feet and a 60 pound bag about 0.45 cubic feet, so the bag counts come from the cubic feet, not the yards. Add about 10 percent for spillage and an uneven subgrade. Hand mixing bags is reasonable up to about half a cubic yard; above that, ready mix delivered by truck is usually cheaper.

Worked example (Stand: 2026)

Slab10 ft × 10 ft, 4 in thick
Thickness in feet (4 ÷ 12)0.333 ft
Volume (10 × 10 × 0.333)33.3 ft³
Cubic yards (33.3 ÷ 27)1.23 yd³
With 10% waste1.36 yd³
80 lb bags (33.3 ÷ 0.6)56 bags
60 lb bags (33.3 ÷ 0.45)75 bags
Ready mix cost (1.36 × $140)$190

Frequently asked questions

How much concrete do I need?

Multiply length by width by the thickness in feet for cubic feet, then divide by 27 for cubic yards. The calculator above does this and also gives the bag counts and a cost. Add about 10 percent for waste.

How many bags make a cubic yard?

A cubic yard is 27 cubic feet. At about 0.6 cubic feet per 80 pound bag that is roughly 45 bags, or about 60 of the 60 pound bags. For anything more than half a yard, ready mix is usually the better call.

How thick should a slab be?

Patios and walkways are usually 4 inches. Driveways for cars are 4 to 5 inches, and 5 to 6 inches if heavier vehicles will park on them. Footings are deeper, often 8 to 12 inches. Check your local code.

What does ready mix concrete cost?

Roughly 120 to 170 dollars per cubic yard delivered in 2026, national average near 140, before any short load fee for orders under the supplier minimum. Set your own quoted price above for an exact total.

Does this calculator store my numbers?

No. Everything is calculated in your browser. Nothing you enter is sent to a server or saved.

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