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Everyday Calculators

Paint Calculator

Estimate the paint needed for a rectangular room. The calculator works out the wall area, removes doors and windows, multiplies by the number of coats and divides by the paint’s coverage.

Units
m
m
m
m²/L

Check the tin; 8–12 m² per litre per coat is typical.

Paint needed7.77 LBuy about 8 L (rounded up)
Paintable area
38.84 m²
Wall area before openings
43.74 m²
Doors and windows removed
4.9 m²
Step-by-step working
  1. Walls = 2 × (4.5 + 3.6) × 2.7 = 43.74 m²
  2. Subtract 1 door(s) at 1.9 m² and 2 window(s) at 1.5 m²
  3. Paint = 38.84 × 2 coats ÷ 10 = 7.77 L

Assumes a standard door of about 1.9 m² and window of 1.5 m². Rough or porous walls and dark-to-light colour changes may need more paint or a primer.

How to use the Paint Calculator

  1. Choose units.
  2. Enter the room dimensions and count doors and windows.
  3. Set the number of coats and the coverage printed on the tin.
  4. Press Calculate.

Formula

Paintable area = 2 × (length + width) × height − doors − windows (+ ceiling).

Paint = area × coats ÷ coverage.

Examples

  • 4.5 × 3.6 m room, 2.7 m high, 1 door, 2 windows, 2 coats at 10 m²/L: 43.74 − 4.9 = 38.84 m² → 7.77 L.

Frequently asked questions

Do I need a primer?

Usually for new plaster, bare wood, patched areas or a big colour change. Primer has its own coverage rate.

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