Room Details
Your Estimate
Total Wall Area
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Deduction for Doors / Windows
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Net Paintable Area
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Total Recommended Litres of Paint
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Paint Can Buyer's Guide
Standard tin sizes to buy at the store
Total purchased
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How this calculator works
This tool estimates the amount of paint needed to cover the walls of a rectangular room. It follows these steps:
- Calculate total wall area — For a rectangular room, the four walls add up to: 2 × (Length + Width) × Height.
- Subtract openings — Each door and window area is deducted from the total wall area (2 m² / 21 sq ft per door, 1.5 m² / 16 sq ft per window).
- Account for multiple coats — The net paintable area is multiplied by the number of coats you plan to apply.
- Convert to volume — The total coated area is divided by the paint's coverage rate.
- Add a waste buffer — A 10% extra allowance is added to cover spills, touch-ups, and uneven surfaces.
Worked example
Suppose you have a room that is 4 m long, 3 m wide, and 2.4 m high, with 1 door, 1 window, applying 2 coats of paint with a coverage of 10 m²/L:
- Total wall area = 2 × (4 + 3) × 2.4 = 33.6 m²
- Deductions = (1 × 2) + (1 × 1.5) = 3.5 m²
- Net paintable area = 33.6 − 3.5 = 30.1 m²
- Total coated area = 30.1 × 2 coats = 60.2 m²
- Litres before buffer = 60.2 ÷ 10 = 6.02 L
- With 10% buffer = 6.02 × 1.10 = 6.62 L (see Buyer's Guide for tin sizes)
Disclaimer
Paint coverage varies significantly between brands, finishes (matte, satin, gloss), and surface types (new plaster, previously painted, textured walls). Always check the coverage figure on your chosen paint tin and consider buying slightly more than calculated. This calculator provides an estimate only and should not replace manufacturer guidance or professional advice.