How to Estimate Painting Costs for a Room
Calculate paintable wall area, paint quantity and labour for interior painting, with the formula and a worked example.
The formula
Wall area = 2 × (length + width) × height. Subtract doors and windows. Paint litres = area × coats ÷ coverage per litre.
Worked example
A 12 × 10 ft room with a 10 ft ceiling has 440 sq.ft of wall. Less one door (21 sq.ft) and two windows (32 sq.ft) leaves 387 sq.ft. Two coats at 120 sq.ft per litre needs about 6.5 litres.