Building calculators

Why the working is shown

Every calculator in this section prints its intermediate volume, the allowances applied, and the density or bag yield used to get from volume to what you actually buy. That is deliberate. A material estimate you cannot check is a material estimate you cannot trust, and the errors are not always small — the two most common ones in this category are quietly severe.

The first is treating poured steps as one block per step. A solid stair is a triangular number of the rise, so a five-step flight needs three times the concrete that the simple version reports. The second is converting volume to tons by relabelling cubic yards, which understates a gravel order by about 35% because crushed stone weighs roughly 1.35 tons per cubic yard, not one.

The volume maths here is a single shared module with a test suite that checks every shape against hand-computed references, including both of those cases. Densities and yields are listed on the material weight chart and the bags per cubic yard page.

What these estimates do not cover

Quantities only. Footing depth depends on your frost line, retaining walls over four feet need engineering, slab reinforcement depends on load, and all three are set locally. Where a code figure is relevant it is cited on the page, but your building department has the number that counts.