Paint Calculator
Paint Calculator
Estimate how much paint you need for walls and ceilings. Choose what you're painting, subtract openings if you want, then apply coats, coverage rate, and a waste allowance for touch-ups. Results include can-size breakdowns.
Paint Calculator
Estimate paint for walls/ceiling using coats, coverage rate, and waste allowance
Results
Enter dimensions above to calculate
Room Area Visualised
The calculator "unfolds" the room to sum all wall faces plus the ceiling. Openings are subtracted from this total net area.
Step-by-Step Formulas
1. Calculate Paint Area
For a rectangular room, wall area is the perimeter multiplied by the height. Add ceiling area when painting it too. Use Custom Area for non-rectangular rooms by measuring each section and adding them up.
2. Subtract Openings (Optional)
Subtract windows, doors, or large areas that won't be painted. If unsure, leave it as 0 and rely on the waste allowance — it's better to overestimate slightly than to run out mid-job.
3. Apply Coats and Coverage Rate
Coverage varies by product and surface type. Always use the coverage figure printed on your paint tin or product datasheet. Typical interior wall paint: 10–12 m²/L or 350–400 ft²/gal.
4. Add Waste Allowance
Waste covers roller loss, cut-ins, touch-ups, and porous or uneven surfaces. 5–15% is typical depending on the surface condition and application method.
Typical Coverage Rates by Paint Type
| Paint type | Metric (m²/L) | Imperial (ft²/gal) |
|---|---|---|
| Interior emulsion (low sheen) | 10–14 m²/L | 350–480 ft²/gal |
| Interior flat / matt | 9–12 m²/L | 320–420 ft²/gal |
| Exterior paint (first coat) | 8–10 m²/L | 280–350 ft²/gal |
| Exterior paint (top coat) | 10–14 m²/L | 350–480 ft²/gal |
| Primer / sealer (bare drywall) | 7–10 m²/L | 250–350 ft²/gal |
| Gloss / semi-gloss trim | 12–15 m²/L | 420–520 ft²/gal |
* Coverage figures are indicative. Always use the theoretical coverage stated on your paint tin or product datasheet.
Worked Example
Paint walls + ceiling in a 5 m × 4 m room, 2.4 m high. Subtract 4 m² of openings. 2 coats, 10 m²/L coverage, 10% waste.
💡 Pro tip
Always buy from the same batch (date code) to avoid sheen/colour variation between cans. Store leftover paint for touch-ups — sealed tightly and stored at room temperature, most interior paints last 2–5 years.
Frequently Asked Questions
- How many coats should I use?
- Two coats is common for most interior paint jobs. You may need more for strong colour changes, new drywall, or high-porosity surfaces. Always follow the paint manufacturer's guidance.
- Should I subtract windows and doors?
- You can subtract large openings for a tighter estimate. Many leave openings as 0 and use a waste allowance instead, especially if there are touch-ups and cut-ins.
- Why is my paint coverage different from the default?
- Coverage depends on the product, sheen, substrate, and wall texture. The most accurate value is on your paint can or product datasheet.
- How do I convert coverage from m²/L to ft²/gal?
- 1 m²/L ≈ 40.75 ft²/US gal. The calculator converts this automatically when switching between metric and imperial.