Concrete Calculator
The Concrete Calculator estimates how much concrete you need for a slab, footing, or pad based on its dimensions, and converts that volume into bags of pre-mixed concrete.
Advertisement
Advertisement
How This Tool Works
Enter your slab's length, width, and thickness, then choose a bag size to see how many bags to buy — or the cubic yards to order for a ready-mix delivery.
Formula & Method
Volume (cubic feet) = length × width × (thickness in inches ÷ 12). Cubic yards = cubic feet ÷ 27. Bags = cubic feet ÷ bag yield (a 60 lb bag yields about 0.45 cu ft).
Example Calculation
A 10×10 ft patio slab at 4 inches thick needs 33.3 cubic feet (1.23 cubic yards) of concrete — about 74 bags of 60 lb concrete.
Frequently Asked Questions
How thick should a concrete slab be?+
Standard patios and walkways use 4 inches, while driveways for vehicles typically need 5–6 inches for durability.
When should I order ready-mix instead of bags?+
For pours over about 1 cubic yard, ready-mix delivery is usually faster and more cost-effective than mixing dozens of bags by hand.
Does this include a base layer?+
No, this calculates concrete volume only. Most slabs also need a compacted gravel base, calculated separately with our Gravel Calculator.
Advertisement
Related Tools
Post Hole Concrete Calculator
Calculate concrete bags needed to set fence or deck posts.
Use tool →ConstructionCubic Yard Calculator
Convert length, width, and height into cubic yards for any bulk material.
Use tool →ConstructionRebar Calculator
Estimate linear feet and sticks of rebar for a concrete slab grid.
Use tool →ConstructionLumber Board Feet Calculator
Calculate board feet for lumber pricing and ordering.
Use tool →