Paint + Primer Coverage Calculator Canada — Litres & Leftover
Painting a room? This free paint and primer coverage calculator helps Canadian homeowners and contractors work out exactly how much paint and primer a room needs — and unlike other calculators, we show you exactly how much you'll have left over for future touch-ups. Enter your room dimensions or wall area directly, choose your surface type, number of coats, and paint tier, and get an instant breakdown in feet and Canadian dollars, sized to the 3.78L cans stocked by Home Depot Canada. Results update live and include a full cost breakdown.
How to use this calculator
1. Measure your room or enter wall area directly
Grab a tape measure and get the length and width of the room in feet, plus the ceiling height — 8 ft is the default and standard for most Canadian homes, but adjust it if yours runs taller. Prefer to skip the geometry? Switch to the "By wall area" tab and enter your total square footage directly. Toggle "Paint ceiling too?" on if you're covering the ceiling in the same colour, since that adds real square footage to your total.
2. Choose your surface type and number of coats
Pick the surface that matches your walls: bare drywall, previously painted, textured, or masonry. This matters more than most people expect — bare drywall soaks up close to 30% more paint per gallon-equivalent than a smooth, previously painted wall, because the drywall paper and joint compound are porous. Then set your number of coats. Two coats is the default and the right call for most repaints. Drop to one coat only for a very close colour match on a wall already in good shape; bump to three over a dark colour.
3. Pick a paint tier and primer option
Choose economy, mid, or premium paint — this changes both the price and the coverage rate, since better paint carries more solids and spreads further. Leave "Include primer?" on Auto and the calculator recommends primer for bare drywall automatically, skipping it for previously painted walls in good condition. If you're covering a dark wall with a light colour, force primer on regardless of surface — it saves you a third topcoat later.
4. Review your paint, primer, and leftover estimate
Results update live as you type. You'll see your paintable area after doors and windows are subtracted, the paint needed for your chosen coats, and how much to buy — rounded up to the nearest 3.78L can, the standard size stocked at Home Depot Canada. Below that is our leftover box: how much paint you'll have left after the job, in litres and in square feet of future touch-up coverage — the number most calculators skip entirely.
The formula we use
Here's the exact math, start to finish. First we work out your wall area: perimeter × height, using 2 × (length + width) × ceiling height, in feet — Canadian construction still runs on imperial for framing and drywall. Painting the ceiling too adds length × width on top. Next we subtract openings — 20 sqft per door and 15 sqft per window, standard sizes for a residential interior door and window — to get your paintable area.
From there: paintable area ÷ coverage rate = paint needed per coat, multiplied by your number of coats. Coverage rate comes from the same matrix used across every region — previously painted drywall at mid-tier covers 400 sqft per gallon-equivalent, bare drywall at the same tier only 300, because raw drywall is more porous. These figures sit below what some tins advertise, on purpose: real walls have texture and roller variance working against them, so we'd rather you buy slightly more than run short mid-coat.
Finally, even though the math runs in imperial, Canadian cans are metric — 3.78L, not a US gallon exactly — so we convert your total to litres and round up to the nearest whole can. That rounding gap is exactly where the leftover figure comes from.
A worked example
Let's walk through a real bedroom: 12 ft × 12 ft, 8 ft ceilings, previously painted walls, one door, two windows, mid-tier paint, two coats.
Wall perimeter: 2 × (12 + 12) = 48 ft. Wall area: 48 × 8 = 384 sqft. Subtract openings: 1 door (20 sqft) + 2 windows (30 sqft) = 50 sqft. That leaves 334 sqft of paintable area.
Previously painted drywall at mid-tier covers 400 sqft per gallon-equivalent, so one coat needs 334 ÷ 400 = 0.835 gallon-equivalents. Two coats: 1.67. Converted to litres and rounded up to whole 3.78L cans, that's 2 cans (7.56L) of Behr Premium Plus at C$47.47 each — C$94.94, which we round to C$95.
Those 2 cans cover a bit more than two coats strictly need, leaving roughly 1.2L of touch-up coverage — enough for scuffs and nail holes for a while yet. Previously painted walls in good condition don't need primer, so C$95 is your full paint cost for the room, no primer line to add. Note that the math runs in imperial feet throughout, and only converts to litres at the very last step, when it's time to match what's actually on the shelf.
Regional cost context
Canadian paint prices are, surprisingly, not inflated by the tariff premium you'll see on some other building materials in this project — worth knowing if you're budgeting against US prices you've seen online.
Estimates are for planning purposes only. As an Amazon Associate we earn from qualifying purchases. In Ontario, retaining walls over 1 m may require engineered design (OBC Part 4), and drops over 600 mm require a guardrail (OBC 9.8.8). Verify permits with your municipality before starting work.
| Product | Tier | Price | Container |
|---|---|---|---|
| Economy | Economy | C$32 | 3.78L |
| Mid | Mid | C$47.47 | 3.78L |
| Premium | Premium | C$79.97 | 3.78L |
| Primer | Zinsser Bulls Eye 1-2-3 | C$50 | 3.78L |
Prices from Home Depot Canada, current as of our last check — see our Methodology page for sources and verification dates.
CIL Smart3, an economy interior line, runs around C$32 for a 3.78L can — a reasonable pick for rentals or ceilings, though we'll flag that this figure is estimated from limited retailer data rather than a direct current listing, so treat it as directional and confirm in-store. Behr Premium Plus at C$47.47 for 3.78L is the mid-tier standard, and its price actually converts to slightly less per litre than the equivalent US can — local production and retail positioning, not a discount. Behr Marquee (deep base) at C$79.97 for 3.78L is the premium option, marketed as a thicker paint-and-primer-in-one.
Zinsser Bulls Eye 1-2-3 primer, at C$50 for 3.78L, costs more per litre than economy or mid-tier paint — primer is a specialty stain-blocking product, not a cheap add-on. All figures reflect our last Home Depot Canada check (see Methodology); expect some regional variation, especially outside Ontario.
Shop on Amazon: Behr Marquee interior paint · Zinsser Bulls Eye 1-2-3 primer
A quick safety note: lead paint
Canada began restricting lead in interior paint in the 1970s, with tighter limits following over the next two decades — so homes built before 1990, and especially before 1976, are the ones to be cautious with. If you're sanding or stripping old paintwork on trim, doors, or older plaster walls, test first rather than assume, and take extra care with dust and disposal — wet methods beat dry sanding on any layer you're unsure about. Health Canada publishes current guidance on lead paint if you're working on an older property and want specifics for your situation.
Common mistakes to avoid
- Skipping primer on bare drywall. New drywall is porous and drinks your topcoat unevenly, leaving flat spots and wasted paint. Primer first, always, on anything unpainted.
- Forgetting to subtract doors and windows. A room with two windows and one door has 50 sqft less wall than its raw perimeter × height suggests — miss that and you'll misjudge both your total and your leftover.
- Assuming a "gallon" is on the shelf. Canadian cans are labelled in litres — 3.78L, not a US gallon can — so if you're used to shopping south of the border, ask for the 3.78L size specifically rather than "a gallon."
- Buying paint across two trips without checking the batch number. Even the same colour and tier can shift slightly between production runs. Buy everything you need in one trip if you can.
- Rounding down "to save money." If the math says 1.67 gallon-equivalents, that's 2 full cans in the real world — running short mid-wall means a hardware store trip while wet paint dries unevenly without you.
- Planning a bigger project? If you're also building a deck, see how many boards you'll need with our composite decking calculator. Adding a retaining wall to the yard too? Check our retaining wall block calculator for blocks and gravel.
Advertisement
Frequently asked questions
How much paint do I need for a room?
For a 12×12 room with standard 8 ft ceilings, budget 2 cans (7.56L total) of paint for two coats on previously painted walls. Canadian cans are sold in 3.78L sizes rather than a US-style gallon, so the calculator converts your gallon-equivalent math to litres at the very last step and rounds up to whole cans. Bare drywall or a big colour change will need more — use the calculator above for your exact room dimensions.
How many square feet does a can of paint cover?
A 3.78L can covers roughly the same area as a US gallon can, since it's essentially the same size — between 250 and 450 sqft depending on surface and tier. Previously painted drywall covers 350-450 sqft per can; bare drywall covers only 250-350 sqft, since raw drywall is more porous. These are deliberately conservative numbers versus what some tins advertise, since real walls have texture and roller variance that lab-measured rates don't account for.
Do I need a separate primer coat?
Bare drywall always needs primer — yes, for anything unpainted. It seals the porous drywall paper and joint compound so your topcoat covers evenly rather than soaking in and looking patchy. Previously painted walls in good condition usually don't need it, unless you're covering a dark colour with something much lighter. Our calculator recommends primer automatically based on your surface type, and you can override it to force primer on for a big colour change.
How many litres or gallons for two coats?
For a 12 ft × 12 ft room with previously painted walls, two coats need 1.67 gallon-equivalents, which converts to about 6.3 litres — rounded up to 2 full 3.78L cans (7.56L) since Canadian paint sells by the can, not the litre. One coat alone needs about 0.84 gallon-equivalents for the same room. Two coats is standard for most repaints; bare drywall or a dramatic colour change may need a third.
How much paint should I buy for touch-ups?
You don't need to buy extra — the leftover from rounding up to whole 3.78L cans usually covers it. For a 12×12 room, 2 cans (7.56L) cover more than the 6.3 litres two coats actually need, leaving roughly 1.2L for touch-ups on scuffs and nail holes down the line. Our calculator shows this leftover figure — in litres and square feet of future coverage — for every project, so you're not guessing how much to keep on hand.
Advertisement
Estimates are for planning purposes only. As an Amazon Associate we earn from qualifying purchases. In Ontario, retaining walls over 1 m may require engineered design (OBC Part 4), and drops over 600 mm require a guardrail (OBC 9.8.8). Verify permits with your municipality before starting work.
Last updated: August 2026. Estimates are for planning purposes only. Verify with local suppliers before purchase. Coverage rates are generic averages; actual coverage varies by product, application method, and surface condition — check your specific paint can's label before buying.