Paint Calculator
Paint Calculator
Last Updated On
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
Paint to buy (+waste)
11.00 L
Net area
50.00 m²
Coverage varies by product, substrate, and texture. Defaults are typical for interior walls; always check your paint tin/datasheet.
Step-by-Step Calculation
Step 1 — Paintable area
2 × (4 + 3.5) × 2.4 + 4 × 3.5 = 50.00 m²
Step 2 — Paint for all coats
50.00 m² × 2 coats ÷ 10.0 m²/L = 10.00 L
Step 3 — Add waste
10.00 × (1 + 10.0%) = 11.00 L
Step 4 — Containers
11 × 1 L, 3 × 4 L, or 2 × 10 L
Result — buy 11.00 L of paint
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.
Coverage, Coats and Surface
The spread rate on the tin assumes ideal conditions that most real walls do not meet:
- Two Coats Is the Realistic Default: One coat rarely gives even colour or full hide, especially over a colour change. Estimating on two coats from the start avoids a mid-job trip for more paint.
- Deducting Openings Is Worth It: Doors and large windows remove real area. A room with a patio slider and two windows can easily lose 60 ft² of wall, which is a meaningful fraction of a gallon.
- Porous Surfaces Destroy Coverage: New drywall, bare plaster, and rough masonry can absorb 30–50% more than the stated rate. Priming first is cheaper than burning topcoat into a thirsty substrate.
Example Calculations
Three scenarios worked through step by step:
Example 1 — Bedroom Walls, Two Coats
Room 12 ft × 14 ft × 9 ft high, 60 ft² openings, 2 coats, 400 ft²/gal.
Perimeter = 2 × (12 + 14) = 52 ft
Wall area = 52 × 9 = 468 ft²
Net area = 468 − 60 = 408 ft²
Two coats = 408 × 2 = 816 ft²
Paint = 816 ÷ 400 = 2.04 → 2 gallons plus a quart
Example 2 — Ceiling Only
Ceiling 12 ft × 14 ft, 2 coats, 350 ft²/gal (flat ceiling paint).
Ceiling area = 12 × 14 = 168 ft²
Two coats = 168 × 2 = 336 ft²
Paint = 336 ÷ 350 = 0.96 gallons
Result: 1 gallon covers it with a little to spare
Example 3 — New Drywall, Primer Plus Topcoat
Walls 600 ft² net, 1 primer coat at 300 ft²/gal, 2 topcoats at 400 ft²/gal.
Primer = 600 ÷ 300 = 2.0 gallons
Topcoat area = 600 × 2 = 1,200 ft²
Topcoat = 1,200 ÷ 400 = 3.0 gallons
Result: 2 gal primer + 3 gal finish
Priming first is what keeps topcoat consumption predictable
Painting Tip
Painting Tip
Buy all the paint for one continuous surface in a single purchase and, if it is more than a couple of gallons, have the store box it — mix the cans together in a larger pail before you start. Tinted paint varies slightly between batches, and boxing guarantees the wall you finish matches the wall you started.
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.
- 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.
- How much does a gallon of paint cover?
- About 350 to 400 square feet per coat on a smooth, primed, previously painted surface. Textured walls, bare drywall, and rough masonry drop that substantially — sometimes to 200 ft² — because the surface holds more paint in its profile.
- How many coats of paint do I need?
- Two is standard and what you should estimate on. One coat may suffice when repainting the same colour in the same sheen. Dramatic colour changes, especially dark to light or over strong reds, can need three plus a tinted primer.
- Should I subtract windows and doors?
- Subtract the large ones — doors, sliders, picture windows. Small windows are often left in as a built-in cushion, since you will lose some paint to cutting in around them anyway. The calculator lets you enter whatever opening total you prefer.
- Do I need primer?
- Yes on bare drywall, new plaster, bare wood, and any patched area, and when making a big colour change or painting over stains. Primer seals porosity so the topcoat covers at its rated spread rate instead of soaking in.
- How do I calculate wall area for a room?
- Multiply the room perimeter by the ceiling height. For a 12 × 14 ft room the perimeter is 52 ft, so at 9 ft high the walls total 468 ft² before deducting openings. This is quicker and less error-prone than measuring each wall.
- How much paint do I need for a 12x12 room?
- With 9 ft ceilings the walls are about 432 ft² gross. Allowing roughly 50 ft² of openings and two coats, that is about 765 ft² of coverage, or two gallons at 400 ft² per gallon. Add a gallon if you are also doing the ceiling.