Concrete Calculator

How to Calculate Concrete for Your Project

Ordering the right amount of concrete saves money and prevents project delays. Whether you are pouring a patio slab, setting fence post columns, or building steps, this calculator provides accurate volume estimates in the units you need. It supports three common shapes and converts between cubic feet, cubic yards, and cubic meters.

Calculation Formulas

For a slab, volume equals length times width times depth. Remember to convert depth from inches to feet by dividing by 12. For a column, use the cylinder formula: pi times radius squared times height. For steps, each step is treated as a rectangular volume using rise, run, and width, with volumes accumulated from bottom to top since lower steps support the ones above.

Bags vs. Ready-Mix

For small projects under 1 cubic yard, pre-mixed bags are practical. A 60-pound bag yields about 0.45 cubic feet and an 80-pound bag about 0.6 cubic feet. For larger projects, ordering ready-mix concrete by the truck (minimum usually 1 cubic yard) is more cost-effective and provides a consistent mix.

Always order 5-10% more concrete than calculated to account for spillage, uneven subgrade, and form imperfections. It is better to have a small amount left over than to run short mid-pour, which can compromise the structural integrity of the finished product.