Concrete Calculator

Enter the dimensions of your slab, footing, or pad. The calculator returns concrete volume and an approximate count of 80 lb pre-mixed bags for small pours.

Last updated: May 14, 2026Reviewed by MaterialNeeded Editorial Team, Editorial review for field workflows and ordering assumptions.

For larger pours, compare results with the ready mix concrete calculator. For reinforcing steel, use the rebar calculator. For boards used in bracing and temporary forms, see the lumber calculator.

Step 1: Units

Step 2

Enter project measurements

Use decimals if needed (e.g. 3.5).

Length (ft)Width (ft)Depth / thickness (in)Imperial: inches. Metric: enter thickness in meters (e.g. 0.1 for about 4 in).

Step 3

Waste allowance (%)

How to use this calculator

Measure the longest inside dimensions of your forms. Enter depth as the finished thickness. Add a waste percentage if the site is uneven or spillage is likely.

What the math is doing

Volume equals length × width × height, converted to cubic yards or cubic meters. Bag counts divide that volume by a typical 80 lb bag yield (about 0.45 cubic feet).

How to measure

Use a tape on parallel inside faces of the forms. For slopes, measure average depth or break the pour into simple rectangles.

Frequently asked questions

How much extra concrete should I order?

For flatwork, 5–10% extra is common. Irregular ground or long pump lines may need more.

Is bag count exact?

No. Manufacturers publish yield per bag; use this tool as a planning estimate and round up.

When should I order ready-mix instead?

Generally over roughly 1 cubic yard on site, ready-mix is less labor than hand-mixing bags.

Does this include reinforcement?

No. Rebar and mesh are separate; use the rebar calculator for grid steel.