Formula
Tiles = (area / tile area) × (1 + wastage). Grout volume = area × joint-area fraction × grout depth, where the joint fraction = ((L + joint)(W + joint) − L·W) / ((L + joint)(W + joint)); grout mass uses 1600 kg/m³.
Standard / source
Standard tiling estimating practice (10% cutting wastage is the usual starting allowance). Grout coverage ultimately comes from the grout maker's datasheet for the actual product — check it before ordering.
Worked example
10 m² of 300 × 300 mm tiles, 3 mm joint, 8 mm depth, 10% wastage: tiles = 10/0.09 × 1.10 ≈ 122.22, so order 123. Joint fraction = (303² − 300²)/303² ≈ 0.0197; grout ≈ 10 × 0.0197 × 0.008 × 1600 ≈ 2.52 kg.
Safety note
Ordering estimate only. Order all tiles from one batch where possible — shade varies between batches — and confirm the grout maker's coverage and the substrate preparation requirements.