Paint Calculator
Plan the paint run before the roller is wet. Enter the room length, width and height in feet, choose the number of coats, set the coverage rate from the can, and add the price per gallon. The calculator totals wall plus ceiling area, multiplies by coats, rounds up to whole gallons, and estimates the paint cost.
How the paint estimate is calculated
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1
Measure the room
Use length, width and ceiling height in feet. If you measured in metres, convert first.
-
2
Set the coats
Two coats are standard for most interior walls. Strong colour changes often need three.
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3
Enter coverage
Use the label rate in square feet per gallon. 350 sq ft per gallon is a cautious wall-paint average.
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4
Add the price
Use the price per gallon, or convert litre pricing to a per-gallon equivalent.
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5
Read the rounded result
The tool includes walls and ceiling, multiplies by coats, then rounds up to whole gallons.
Coverage rates
| Paint or surface type | Typical coverage to enter |
|---|---|
| Flat or matte wall paint | 375-400 sq ft/gal |
| Eggshell interior paint | 350-375 sq ft/gal |
| Satin or semi-gloss | 325-350 sq ft/gal |
| Gloss enamel or trim paint | 300-325 sq ft/gal |
| Primer or sealer | 250-300 sq ft/gal |
| Textured plaster or masonry | 200-250 sq ft/gal |
Manufacturers list coverage on the can. Smooth, previously painted drywall often lands near 350-400 sq ft per gallon, while primer and textured surfaces need a lower number.
Metric conversions
| Label on the can | Enter in the calculator |
|---|---|
| 8 m²/L | 326 sq ft/gal |
| 9 m²/L | 367 sq ft/gal |
| 10 m²/L | 407 sq ft/gal |
| 11 m²/L | 448 sq ft/gal |
| 12 m²/L | 489 sq ft/gal |
Use 1 m = 3.28084 ft for room dimensions and 1 m²/L = 40.7 sq ft/gal for coverage. One US gallon is 3.785 L.
What is included
| Input | How it is used |
|---|---|
| Length and width | Ceiling area |
| Length, width and height | Wall area |
| Coats | Multiplies the total paintable area |
| Coverage | Converts coated area to gallons |
| Price per gallon | Estimates material cost |
The calculator does not subtract doors, windows, cabinets or baseboards. For rooms with lots of glass or built-ins, treat the rounded-up result as a buying guide and check the can size before checkout.
Worked example
A 12 ft × 15 ft room with an 8 ft ceiling, walls plus ceiling, two coats, and coverage set to 350 sq ft/gal.
- Wall perimeter: 2 × (12 + 15) = 54 ft
- Wall area: 54 × 8 = 432 sq ft
- Ceiling area: 12 × 15 = 180 sq ft
- One coat: 432 + 180 = 612 sq ft
- Two coats: 612 × 2 = 1,224 sq ft
- Gallons: 1,224 ÷ 350 = 3.5, so the calculator rounds up to 4 gallons
Tips for an accurate estimate
- Round up to real can sizes. A little leftover paint is useful for touch-ups.
- Buy the same batch. Colour and sheen can vary between batches, especially with deep colours.
- Use primer when the surface changes. New drywall, bare wood, stains and dark-to-light colour changes usually need primer.
- Separate trim if quality matters. Trim paint often has different coverage and comes in quarts rather than gallons.
- Check ceiling paint. Flat white ceiling paint may cover more than wall paint, but stained or textured ceilings may cover less.
When to hire a pro
Bring in a professional when the job involves high stairwells, exterior access, spraying, water damage, heavy surface repair, or older coatings that may need specialist handling. For ordinary bedrooms and living rooms, the calculator is usually enough to plan the shopping list.
Frequently Asked Questions
Use primer for bare drywall, new plaster, bare wood, stains, or a dark-to-light colour change. For a similar colour over clean washable paint in good condition, primer may not be necessary.
Two coats are the normal planning number. Plan three for deep colours, light paint over a dark wall, uneven absorbent surfaces, or when the paint label recommends it.
Yes. Convert the label coverage from m²/L to sq ft/gal by multiplying by 40.7. For example, 10 m²/L is about 407 sq ft/gal.
This tool does not subtract openings. In most rooms, rounding up to full gallons already leaves some working room. If a wall is mostly glass or cabinets, calculate that area separately before buying.
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