Methodology

Every formula works in metric units. Imperial entries are converted to metric first and results converted back for display.

Gallons are US gallons. Tons in imperial display are US short tons (2,000 lb), while internal weights are metric tonnes (1,000 kg), so the two differ by about 10%. Check which one your supplier uses.

Paint coverage uses m²/L in Metric and ft²/US gal in Imperial. To convert ft²/US gal to m²/L, multiply by 0.09290304 and divide by 3.785411784.

Areas are rectangles: width × height or width × length. Wall area subtracts doors at 1.89 m² and windows at 1.44 m². Roof area divides the footprint by cos(pitch). Stair area is steps × width × (tread + riser).

Volume is area × depth. Concrete is for slabs on the ground; Foundation uses trench width, length and depth. Gravel, sand, stone and asphalt convert to weight with fixed densities of 1.6, 1.5, 1.5 and 2.4 t/m³. The stone figure reuses the sand density and is therefore rough.

Bricks, tiles, pavers, boards and panels are counted by dividing the covered area by the area of one piece. Brick and mortar joints are added to the brick face. Drywall uses a fixed 1.2 m × 2.4 m panel; mortar uses 0.015 m³ per 25 kg bag; cement uses a fixed 320 kg per m³ in 50 kg bags.

The cement figure is a planning assumption, not a strength specification.

Counts of whole items (bricks, tiles, bags, boards, panels, pavers) are rounded up. Areas, volumes and weights are shown as calculated, so round them up yourself to the pack or delivery size.

Waste is a percentage multiplier (1 + waste/100) applied to the quantity. The default is 10%. Use more for diagonal layouts, small rooms, many cuts or uneven bases. The wall-area calculator has no waste.

Paint uses the single-coat coverage you enter in m²/L or ft²/US gal, converted internally to m²/L. Coverage is a product property that depends on surface and application, so take it from the label. Plaster uses a fixed 1.2 kg per m² per mm.

Roof: one uniform pitch over the projected footprint; no hips, valleys or overhangs. Stairs: only tread plus riser covering area, not a safe stair geometry check. Foundation and concrete: volume only, not structural design. Cement: 320 kg/m³ is fixed.

How to verify: repeat the worked example on a calculator page by hand and compare with manufacturer specifications. Report a suspected error to info@materialcalculator.app.