About Build Calculator

Build Calculator is a set of free calculators for people who build things — contractors estimating a job, and homeowners planning a patio, a fence or a new floor.

How we keep the numbers right

Every calculator runs on one tested calculation module. Before each release an automated test suite checks known answers — for example a 10 × 10 ft slab 4 in thick must give 1.23 cubic yards and 55.42 bags of 80 lb concrete, exactly as the industry references do — plus code tables from the NEC, the IRC and DIN standards.

Material constants (bag yields, densities, coverage rates) come from manufacturers’ data sheets and standards and are written next to each formula, so you can check them.

Estimates, not engineering

Results are estimates for planning and ordering. Always check quantities with your supplier and follow your local building code; structural and electrical work may need a licensed professional.