Paint Calculator
Enter wall area and coats to get the liters of paint and number of cans you need. Auto-deducts doors and windows, includes waste.
Paint needed
4L cans 3 · 1L cans 10
- Openings deducted
- 5 ㎡
- Net paint area
- 45 ㎡
- Total coat area
- 90 ㎡
Standard deduction: door 2m², window 1.5m². Interior water-based paint ~10 m²/L per coat, 2 coats recommended. Adjust spread rate by surface and paint type.
What this tool does
The paint calculator estimates the liters of paint needed from wall area and number of coats. It auto-deducts doors and windows, applies the spread rate (m²/L) and a waste allowance, and tells you how many 4L and 1L cans to buy. Avoid buying too little or too much for DIY painting or quote checks.
Who uses this
- Estimate paint to buy before DIY wall painting
- Cans needed per room or living area
- Total for a 2-coat (primer + finish) job
- Verify a painting quote
- Estimate material for exterior walls or ceilings
How to use
- 1Enter total wall area (m²). Compute as perimeter × height or use a direct measurement.
- 2Enter the number of doors and windows; standard areas (door 2 m², window 1.5 m²) are deducted automatically.
- 3Adjust coats (usually 2), spread rate (interior water-based ~10 m²/L), and waste (10%) to get liters and cans.
Paint quantity formula
Net paint area = wall area − (doors × 2 m² + windows × 1.5 m²) Total coat area = net area × number of coats Paint (L) = total coat area ÷ spread rate (m²/L) With waste = paint × (1 + waste rate) Spread rate (per coat): interior water-based ~10 m²/L, exterior ~8, rough surface ~6 4L cans = ceil(with-waste ÷ 4)
Real examples
Example 1: Room walls 50 m², 1 door + 2 windows, 2 coats
Openings = 2 + 3 = 5 m². Net 45 m². Total coat 90 m². At spread 10 → 9 L; +10% waste → 9.9 L. Buy three 4L cans.
Example 2: Living room 100 m², 2 coats (no openings)
Total coat 200 m² ÷ 10 = 20 L. +10% = 22 L. Six 4L cans. Buy at once to avoid color batch variation.
Example 3: Rough exterior surface
Lower spread rate to 6 m²/L. The same area needs ~1.7× more paint than interior — rougher surfaces absorb more.
Frequently asked questions
How many coats should I apply?+
Two coats (primer + finish) is standard. Use three when covering a dark color with light, or for heavy stains. A same-color refresh can be one coat. A single coat often shows streaks and bleed-through.
How do I choose the spread rate?+
It's printed on the product label as m²/L. Interior water-based paint is ~8-12 m²/L per coat; exterior and rough surfaces are 6-8. Rougher, more absorbent surfaces have a lower spread rate (need more paint).
Why deduct doors and windows?+
They aren't painted wall, so they're excluded from net area. The calculator deducts standard sizes (door 0.9×2.1≈2 m², window 1.2×1.2≈1.5 m²); adjust the area directly if yours differ greatly.
Why a waste allowance?+
Paint absorbed by rollers/brushes, drips, touch-ups, and can residue typically warrant a 10% allowance. For complex shapes or beginners, 15-20% is recommended.
How do I find wall area?+
Perimeter (width+depth)×2 × ceiling height. E.g., a 3m×4m room at 2.4m → 14m × 2.4 = 33.6 m². Add the ceiling (width×depth = 12 m²) if painting it too.
Is primer calculated separately?+
New drywall or painting over a dark color needs primer. Calculate primer with the same area and spread rate separately, or include it as an extra coat in this tool.
Cautions
- •Standard deduction: door 2 m², window 1.5 m². Adjust wall area if your sizes differ.
- •Spread rate varies by product/surface (interior ~10, exterior ~8, rough ~6 m²/L).
- •10% waste is the default; complex shapes or beginners 15-20%.
- •Primer must be calculated separately.
- •Re-verify final quantity against the product label's spread rate.
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Last reviewed: 2026-05-30