Estimate paint quantity from total wall length, wall height, openings, coats and the coverage rate printed on your paint.
Formula
Paintable area = total wall length × wall height − openings. Paint quantity = paintable area × coats ÷ coverage rate.
Example: 20 m of wall × 2.5 m high, minus 4 m² of openings, with 2 coats at 10 m²/L needs about 9.2 L.
Assumption
Use the actual coverage rate from the product label. Surface texture, primer, color change and application method can change real usage.