Disclaimer

Every calculator on ProjectCalc estimates how much material a job needs. None of them design anything. Specifically, ProjectCalc does not perform or replace:

• structural design or load calculations of any kind;
• sizing of beams, joists, lintels, footings or reinforcement;
• assessment of whether a structure can carry a new load or covering;
• electrical, gas, plumbing or drainage design;
• building-code, planning or permit compliance checks;
• site-specific soil, drainage or ground-condition assessment.

Where a calculator sits near one of these boundaries — concrete footings, block walls, roof area, stairs — the page carries its own scope note saying so. Those notes are not boilerplate; read them.

Material estimates depend on assumptions that vary in the real world: bag yields differ between manufacturers, gravel and soil densities change with moisture and compaction, box and pallet quantities are not standardised, and how much of each cut piece becomes waste depends on your layout and your skill with a saw.

We handle this by showing the assumptions on every page and letting you edit the ones that matter, rather than hiding a constant and presenting the output as certain. The methodology page explains how each kind of assumption is chosen and sourced.

Check the result against your own measurements and your supplier's product data. Where a figure is printed on the bag, box or pallet, that figure beats our default. For anything structural or code-related, ask your local building authority, a qualified engineer or a licensed trade.

Some measurements are more dangerous to take than the job is worth. Roof pitch in particular can be measured from inside the attic or from the ground — do not climb a steep or wet roof to use a calculator.