Grout (kg) ≈ (A + B) ÷ (A × B) × joint width × joint depth × area × 1.6, with tile sides A and B in cm, joint in mm and area in m² — 1.6 is the grout density in g/cm³ plus ~10% waste. Thinset is estimated from the trowel notch: a 10–15 mm notch uses roughly one 20 kg bag per 8–9 m².