How Our Concrete Calculator Works

Volume Formulas

Each shape converts inches to feet and computes cubic feet: slab L × W × T; footing L × W × D; round forms 3.1416 × r² × H; post holes subtract the post from the hole; steps stack one block per step.

Units and Conversions

One cubic yard is 27 ft³ and 0.7646 m³ (NIST SP 811). Metric inputs are converted to feet before calculating.

Bag Yields and Rounding

Bag yields come from Quikrete's calculator: 0.6 ft³ (80 lb), 0.45 (60 lb), 0.375 (50 lb) and 0.3 (40 lb). Bag counts always round up, as Quikrete's calculator does.

This Calculator's Own Rules

• 10% waste by default, adjustable from 0 to 15%, inside NRMCA's advice to order 4 to 10 percent extra.
• 150 lb/ft³ design density, inside FHWA's 140–155 range.
• About 1 yd³ as the point where ready-mix beats bags.
• Trucks counted at 12 and 8 yd³, inside NRMCA's 8–12 range.
• Prices default to Concrete Network's $160–195 per yard and are editable.

Tested Examples

These examples are checked against the engine before every release.