Mortar & Grout Calculator

Formula

How this is calculated

First the tiling area is found from the length and width you enter (area = L × W). Thin-set mortar consumption depends mainly on the trowel notch depth: a 6 mm notch spreads roughly 5 kg of adhesive per square metre, so coverage is scaled linearly as 5 × (notch / 6) kg/m². Multiplying coverage by the area gives the mortar mass, and bags are rounded up using a 20 kg bag weight so you never buy short.

Grout fills the joints between tiles. The grout mass per square metre is ((tileL + tileW) / (tileL × tileW)) × jointWidth × jointDepth × density, with all tile dimensions in millimetres. The first factor captures how many joints fall in a square metre (small tiles mean more joints and more grout), the joint width and the joint depth (taken as the tile thickness) give the cross-section, and a density of 1.8 g/cm³ converts joint volume to kilograms. The neat unit trick is that one millimetre of material spread over one square metre equals exactly one litre, so the millimetre product reads directly as litres per square metre before applying density.

These are estimates for planning. Always add about 10 percent for waste, spillage, uneven substrates and partial bags, and check the specific coverage figures printed on your product bag, since formulations vary. Results assume full-coverage thin-set (not spot bonding) and grout that completely fills joints to the tile thickness.