Painting & Walls
Paint Calculator
Enter your room dimensions in metres or feet — Canadian paint is sold in litres, and this calculator converts either way, deducts openings, and counts the cans to buy.
Formula tested · Local units · No sign-up
Project inputs
Enter measurements
Use your preferred units. Results update automatically.
Show the calculation methodFormula, conversions, rounding, and assumptions+
Wall area = 2 × (room length + room width) × wall height, converted to a common unit first. Canadian paint is labelled in litres and m², but many rooms are still measured in feet — the calculator accepts both and converts internally.
Standard openings are deducted: 1.9 m² per door and 1.4 m² per window (editable typical values). The remaining paintable area is multiplied by the number of coats.
Litres = total area ÷ coverage per litre (typical interior paint covers 10–12 m² per litre per coat; the default is 11). Cans are rounded up to whole units — set the container size to match what your store sells, such as the common 3.78 L can.
Real-world example
Worked example: 4 m × 3 m bedroom, 2.4 m ceilings, 2 coats
- Wall area: 2 × (4 + 3) × 2.4 = 33.6 m².
- Deduct openings: 1 door (1.9 m²) + 1 window (1.4 m²) = 3.3 m² → 30.3 m² paintable.
- Two coats: 30.3 × 2 = 60.6 m² to cover.
- Paint needed: 60.6 ÷ 11 m²/L = 5.51 litres.
- With the container size set to a 3.78 L can: 5.51 ÷ 3.78 = 1.46 → round up to 2 cans.
Buy 2 × 3.78 L cans. Enter your store's price per can and your province's combined GST/PST or HST rate for a cost estimate — rates differ by province.
Before you start
How to measure
- Measure length, width and height in whichever units you have — each field accepts metres, centimetres, feet or inches and the tool converts.
- Count doors and windows; the calculator subtracts standard areas (1.9 m² per door, 1.4 m² per window). Measure patio doors and picture windows separately.
- If you measured the room in feet, double-check the unit selector on each field — mixing feet into a metres field is the most common input error.
Local guidance
Notes for Canada
- Canadian paint cans carry bilingual (English/French) labels with coverage stated in litres and square metres, though many stores still talk in gallons — the common large can is 3.78 L, the metric twin of a US gallon.
- Rooms are often measured in feet while paint is sold metric; this calculator accepts both so you don't have to convert by hand.
- Sales tax is 5% federal GST plus provincial tax, or a combined HST, depending on the province — enter your combined rate. Shelf prices are usually shown before tax.
Quick reference
Typical coverage by surface (planning values — check your can)
| Surface | Typical coverage per coat |
|---|---|
| Previously painted smooth drywall | 11–12 m²/L |
| New or primed drywall | 9–11 m²/L |
| Textured or porous surfaces | 8–10 m²/L |
| Rough masonry | 5–8 m²/L |
Editable planning values only — the bilingual label on your can states the coverage that governs.
Good to know
Common mistakes to avoid
- Mixing unit systems mid-calculation — entering a room measured in feet into fields set to metres.
- Assuming a 'gallon' of paint is 4 litres everywhere — the common Canadian can is 3.78 L; set the container size to what your store actually sells.
- Forgetting the tax difference between provinces when comparing online prices.
- Skipping primer on new drywall and then wondering why coverage fell short of the label figure.
Need help?
Frequently asked questions
How much paint for a 10 ft × 10 ft room with 8 ft ceilings?
In metric that's roughly 3.05 m × 3.05 m with 2.44 m walls: wall area ≈ 29.7 m². Deduct one door (1.9 m²) → 27.8 m²; two coats ≈ 55.7 m²; at 11 m²/L that's about 5.1 litres — two 3.78 L cans.
Why does the can say litres when the store calls it a gallon?
Canada sells paint in metric sizes with bilingual labels; the 3.78 L can is the direct metric equivalent of a US gallon, so the old name stuck. Enter the litre size printed on the can as the container size.
What tax rate should I enter?
Your province's combined rate: 5% GST everywhere, plus PST or the provincial portion of HST depending on where you live. The calculator applies whatever rate you enter to the price you enter.
Keep planning
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About this calculator
- Written by:
- BuildMeasure Editorial Team
- Technically reviewed by:
- Pending independent technical reviewer (formula unit-tested; see methodology)
- Last reviewed:
- 2026-07-16
- Formula version:
- 1.0.0
- Region reviewed for:
- Canada
- Spotted an error?
- Report a correction
Methodology
- Wall area comes either from room dimensions (perimeter × wall height, i.e. 2 × (length + width) × height) or from a directly entered area. All arithmetic runs internally in SI units (m² and litres) to avoid unit drift; regional units are converted on the way in and out.
- Standard opening deductions (door and window areas, clearly labelled next to the inputs and editable via the counts) are subtracted from the wall area, floored at zero. The paintable area is multiplied by the number of coats to get the total area to cover.
- Paint volume = total area ÷ the coverage rate you enter. The number of containers is the paint volume divided by your container size, rounded UP to the next whole container, because paint is sold in whole cans.
- The cost estimate multiplies the container count by the price you enter, then applies the tax rate you enter. No prices are built in.
- The formula is covered by automated unit tests, including hand-calculated worked examples, and is versioned (see formula version on this page).
Sources & standards
- Unit definitions: 1 ft = 0.3048 m (exact); 3.78 L is the common Canadian large paint can, matching one US gallon.
- Coverage defaults: 10–12 m² per litre per coat is a typical interior paint label range; the label on your can governs.
This tool provides a material estimate for planning purposes only. It is not a quotation, and it does not assess surface condition, primer requirements or colour-change coverage. Confirm quantities and the coverage rate on your specific product with your paint supplier before buying.