Paint Calculator: How Much Paint, Primer and Putty for a Room

Paint Calculator

Litres of paint, primer and kg of putty for a room or a known wall area.

Unit

Room length

Room width

Wall height

Paint area

Doors (nos)

Windows (nos)

Include ceiling

Coats of paint

Paint coverage per coat (sq ft/litre)

Primer (1 coat)

Wall putty (2 coats)

Sizes and coverage assumptions

Door size (sq ft)

Window size (sq ft)

Primer coverage (sq ft/litre)

Putty coverage, 2 coats (sq ft/kg)

Door 7 × 3 ft and window 4 × 4 ft by default. Check the coverage printed on your paint bucket.

Free tool by EngineeringNepal.com.np · Results are for guidance; check critical figures with a qualified engineer.

How much paint do I need for a room?

Paint quantity depends on the area to be painted, the number of coats and the coverage of the paint. For a room, the wall area is the perimeter × height, plus the ceiling if you are painting it, minus doors and windows. Divide by the coverage per litre and multiply by the number of coats.

Formula

Paint (litres) = paintable area × coats ÷ coverage per coat

Example: a 14 × 12 ft room with 10 ft walls has 520 sq ft of walls and 168 sq ft of ceiling. After deducting one door (21 sq ft) and two windows (32 sq ft), about 635 sq ft remains. Two coats at 110 sq ft per litre need about 11.5 litres.

Typical coverage

Product	Coverage (approx.)
Interior emulsion, per coat	100 to 120 sq ft per litre
Exterior emulsion, per coat	60 to 90 sq ft per litre
Primer	90 to 110 sq ft per litre
Wall putty, 2 coats	15 to 20 sq ft per kg

Rough and new plastered walls absorb more paint, so use the lower coverage figure.

Frequently asked questions

Do I need putty and primer?

Putty gives a smooth finish on new plaster and fills fine cracks. Primer seals the surface so the finish coat covers evenly and lasts longer. For repainting a wall in good condition, putty can often be skipped.