Concrete Calculator
Calculate exactly how much concrete you need for slabs, columns, footings, and stairs. Get cubic yards, bag counts, and cost estimates.
How It Works
Understand how concrete volume is calculated for different structures.
Volume Calculation
Concrete volume is length × width × depth for rectangular slabs. Circular slabs use π × r² × depth. Columns use π × r² × height. All measurements are converted to feet, then divided by 27 to get cubic yards.
Bag Count Estimates
An 80lb bag yields about 0.6 cubic feet of concrete. A 60lb bag yields about 0.45 cubic feet. Divide your total cubic feet by these values to get the number of bags needed. Always round up to the nearest bag.
Weight & Mix Design
Concrete weighs approximately 150 pounds per cubic foot. A standard 1:2:3 mix (cement:sand:aggregate) is suitable for most residential projects. Structural applications require a stronger 1:1.5:2.5 mix.
Frequently Asked Questions
Common questions about concrete volume and mixing.
You need 45 bags of 80lb concrete mix to make one cubic yard. Each 80lb bag yields approximately 0.6 cubic feet. For a 60lb bag, you need 60 bags per yard since each yields about 0.45 cubic feet. Always round up and order slightly more concrete than calculated to account for spillage and uneven subgrades.
PSI measures the compressive strength of cured concrete. 3000 PSI concrete is standard for residential slabs, driveways, and sidewalks. 4000 PSI concrete is stronger and more durable, recommended for structural applications like footings, retaining walls, and commercial projects where heavier loads are expected. Higher PSI concrete uses more cement and less water in the mix.
Standard concrete slab thickness is 4 inches for patios, walkways, and residential floors. Driveways should be at least 5-6 inches thick to handle vehicle weight. For heavy trucks or equipment, 6-8 inches is recommended. Interior garage slabs typically require 4-5 inches of concrete over a compacted gravel base with wire mesh reinforcement.