A paint calculator tells you how many gallons or liters of paint to buy for a room. Type the room size, the doors and windows, the number of coats and the coverage on the can, and it works out the wall area, the paint needed, the amount to buy and the cost.
Quick answer: Paint needed = wall area × coats ÷ coverage per gallon. A 14 ft × 12 ft room with 8 ft walls, one door and two windows has 366 sq ft of wall. Two coats at 350 sq ft per gallon need 2.09 gallons, or 2.3 gallons with 10% extra, so you buy 3 gallons.
How to use the paint calculator
The paint calculator works in feet and gallons or in meters and liters. Pick your units at the top of the paint calculator, then follow these steps.
- Type the room length, width and wall height. For several identical rooms, set the number of rooms.
- Enter how many doors and windows there are, and the area of each. The tool subtracts them from the walls.
- Choose 1, 2 or 3 coats and the surface type. Rougher surfaces soak up more paint.
- Check the coverage per gallon (or per liter) printed on your can, or keep the default of 350 sq ft per gallon.
- Tick the ceiling, trim or doors if you are painting them, then read the paint to buy, rounded up to cans, and the cost.
| Input | What it means | Typical value |
|---|---|---|
| Length, width, height | Room size used for the wall perimeter | 14 ft × 12 ft, 8 ft walls |
| Doors and windows | Openings subtracted from the wall area | Door 20 sq ft, window 15 sq ft |
| Coats | How many layers of paint | 2 coats |
| Coverage | Area one gallon covers in one coat | 350 to 400 sq ft per gallon |
| Waste | Extra for roller loss and touch-ups | 10% |
Paint calculator formula for walls
The paint calculator for walls adds up the four walls, takes away the openings, and divides by what a gallon covers. Walls and ceilings use the same idea, and the formula is short enough to do by hand.
- Wall area = 2 × (length + width) × height − doors − windows.
- Paint needed = wall area × number of coats ÷ coverage per gallon.
- Paint to buy = paint needed × (1 + waste %), rounded up to whole cans.
For example, a 14 ft × 12 ft room with 8 ft walls has a perimeter of 52 ft and 416 sq ft of wall. One door (20 sq ft) and two windows (30 sq ft) leave 366 sq ft. Two coats at 350 sq ft per gallon need 366 × 2 ÷ 350 = 2.09 gallons, and 10% extra makes 2.3 gallons, so you buy 3.
Paint calculator square feet: how much paint for common rooms
Here is the paint calculator square feet answer for typical rooms with 8 ft walls, one door and two windows (50 sq ft of openings), at 350 sq ft per gallon with 10% extra. The last column is the whole number of gallons you buy for two coats.
| Room size | Wall area, sq ft | Gallons, 1 coat | Gallons, 2 coats | Gallons to buy (2 coats) |
|---|---|---|---|---|
| 10 × 10 ft | 270 | 0.85 | 1.70 | 2 |
| 10 × 12 ft | 302 | 0.95 | 1.90 | 2 |
| 12 × 12 ft | 334 | 1.05 | 2.10 | 3 |
| 12 × 14 ft | 366 | 1.15 | 2.30 | 3 |
| 12 × 16 ft | 398 | 1.25 | 2.50 | 3 |
| 14 × 16 ft | 430 | 1.35 | 2.70 | 3 |
| 16 × 20 ft | 526 | 1.65 | 3.31 | 4 |
To measure the room, use a tape measure along each wall, or work from the floor area with the square footage calculator. For a non-rectangular room, split it into rectangles with the perimeter and area calculator.
Paint coverage per gallon: what to use
Paint coverage per gallon depends on the product, the surface and how thickly you apply it. Sherwin-Williams says on its paint calculator page that a gallon typically covers about 350 to 400 square feet, which is enough for a 10 ft × 10 ft room, and suggests keeping a little more than a gallon on hand for textured walls. That figure is for one coat, so two coats cover half as much area per gallon.
Always use the coverage printed on your own can or product data sheet. Primer, stain-blocking paint and cheaper paints often cover less. In the tool, the surface menu reduces coverage to 85% for lightly textured or porous walls and 75% for rough surfaces such as bare drywall, brick or stucco.
| Coverage per gallon | One coat covers | Two coats cover | Metric equivalent |
|---|---|---|---|
| 250 sq ft | 250 sq ft | 125 sq ft | 6.1 m² per liter |
| 300 sq ft | 300 sq ft | 150 sq ft | 7.4 m² per liter |
| 350 sq ft | 350 sq ft | 175 sq ft | 8.6 m² per liter |
| 400 sq ft | 400 sq ft | 200 sq ft | 9.8 m² per liter |
To convert, 1 m² per liter equals about 40.7 sq ft per gallon, so 350 sq ft per gallon is 8.6 m² per liter and 400 is 9.8. Labels in the UK and Australia often quote a different figure, so type the number printed on your tin.
How many gallons of paint do I need for a ceiling?
A ceiling has an area of length × width, so the paint calculator for ceiling work is simple: a 14 ft × 12 ft ceiling is 168 sq ft. Two coats need 168 × 2 ÷ 350 = 0.96 gallons, which is 1.06 gallons with 10% extra, so buy one gallon plus a quart, or two gallons if quarts are not sold in your color. Tick the ceiling box and the tool adds it as its own line because ceiling paint is usually a different product.
| Ceiling size | Area, sq ft | Gallons, 1 coat | Gallons, 2 coats |
|---|---|---|---|
| 10 × 10 ft | 100 | 0.31 | 0.63 |
| 12 × 12 ft | 144 | 0.45 | 0.91 |
| 12 × 14 ft | 168 | 0.53 | 1.06 |
| 14 × 16 ft | 224 | 0.70 | 1.41 |
| 16 × 20 ft | 320 | 1.01 | 2.01 |
Trim, baseboards and doors
Trim is measured as a strip: length × width. A 5 in baseboard around a 14 ft × 12 ft room is 52 ft × 5 ÷ 12 = 21.7 sq ft, so one coat takes under a quart. Doors are painted on both sides, so a 20 sq ft door is 40 sq ft of paint. Tick the trim and door boxes, and the paint calculator puts them on a separate line because trim paint is normally a semi-gloss.
Worked examples with the working shown
Example 1: one bedroom, walls only
The room is 14 ft × 12 ft with 8 ft walls, one door and two windows. Walls: 2 × (14 + 12) × 8 = 416, minus 50 = 366 sq ft. Paint: 366 × 2 ÷ 350 × 1.10 = 2.30 gallons. You buy 3 gallons, and at $40 a gallon that costs $120.
Example 2: two bedrooms with ceilings, trim and doors
Two identical 14 ft × 12 ft rooms have 732 sq ft of wall, 336 sq ft of ceiling and 123 sq ft of trim and doors (baseboards plus both sides of the doors). With two coats and 10% extra, the walls need 4.60 gallons, the ceilings 2.11 and the trim 0.78. Buying quarts and gallons, that is 4.75 + 2.25 + 1 = 8 gallons in all.
Example 3: a 4.5 m × 4 m room in meters
With 2.4 m walls, the perimeter is 17 m and the wall area is 40.8 m². One door (1.8 m²) and two windows (2.8 m²) leave 36.2 m². Two coats at 10 m² per liter need 36.2 × 2 ÷ 10 = 7.24 liters, or 7.96 liters with 10% extra. You buy 8 liters, for example two 4 L tins.
How much paint do I need? Waste, coats and extra
Allow about 10% extra for roller loss, cutting in and touch-ups, and keep the leftover for future repairs. Two coats are standard. One coat is only enough when repainting a similar color over a clean, sound surface. Moving from dark to light, or painting new drywall, may need a primer plus two coats of color.
| Surface area | 1 coat | 2 coats | 3 coats |
|---|---|---|---|
| 200 sq ft | 0.6 gal | 1.3 gal | 1.9 gal |
| 400 sq ft | 1.3 gal | 2.5 gal | 3.8 gal |
| 600 sq ft | 1.9 gal | 3.8 gal | 5.7 gal |
| 800 sq ft | 2.5 gal | 5.0 gal | 7.5 gal |
| 1000 sq ft | 3.1 gal | 6.3 gal | 9.4 gal |
| 1500 sq ft | 4.7 gal | 9.4 gal | 14.1 gal |
Primer is a separate product with its own coverage, so calculate it as one coat with a lower coverage figure from the can. Stain-blocking primers and bare surfaces such as new drywall, wood or masonry are the usual reasons to prime before painting, and sanding glossy walls first helps the new coat stick.
Planning ahead saves a second trip, but buy the paint in one batch. Colors tinted in separate batches can differ slightly, so mix several cans together in a larger bucket (boxing) for a uniform finish on a big wall.
Paint cost estimate
Cost is the paint to buy times the price per gallon. Prices vary widely by brand, sheen and store, so the tool uses an example price you can change. The table shows what whole gallons cost at four example prices, so you can see how quickly the budget moves.
| Gallons to buy | $30 per gallon | $40 per gallon | $50 per gallon | $60 per gallon |
|---|---|---|---|---|
| 2 | $60.00 | $80.00 | $100.00 | $120.00 |
| 3 | $90.00 | $120.00 | $150.00 | $180.00 |
| 4 | $120.00 | $160.00 | $200.00 | $240.00 |
| 6 | $180.00 | $240.00 | $300.00 | $360.00 |
| 8 | $240.00 | $320.00 | $400.00 | $480.00 |
Paint calculator by region: US, Canada, UK and Australia
Paint calculator for the United States and Canada
US paint is sold in quarts, gallons and 5 gallon pails, and rooms are measured in feet. Canada uses liters, and cans are often one US gallon equivalent (about 3.78 liters), so use the metric option and your can label. Check the lead rules below before sanding an older home.
Paint calculator for the UK and Europe
Paint is sold in liters, commonly in 1, 2.5, 5 and 10 liter tins, and tins show coverage in m² per liter. The imperial UK gallon is 4.546 liters, so do not mix it up with the 3.785 liter US gallon. Choose the metric option and the UK tin sizes.
Paint calculator for Australia and New Zealand
Paint is sold in liters, with typical tin sizes of 1, 2, 4, 10 and 15 liters, and the label gives coverage in m² per liter. Rooms are measured in meters with 2.4 m ceilings common. The tool picks the smallest combination of tins that covers your total, and you should confirm sizes at your store.
Safety, lead paint and professional advice
The US EPA says about three-quarters of US homes built before 1978 still contain some lead-based paint. If you are sanding, scraping or removing paint in an older home, follow the EPA lead-safe rules or hire a certified renovator, and keep children and pregnant women away from the work area. Ventilate the room, wear a suitable mask when sanding, and follow the can for drying and recoat times.
A paint calculator gives a planning estimate. For large or exterior jobs, new construction or special coatings, ask the paint store or a professional painter to confirm quantities and primer.
Common mistakes with a paint calculator
- Forgetting the second coat. A single coat uses half the paint but rarely hides a color change.
- Using the wrong coverage. Use the number on your can, not a generic one, especially for primer.
- Skipping doors and windows. Not subtracting them overbuys, but painting doors and trim needs its own paint.
- Measuring only the floor. Wall area depends on the perimeter and the height, not the floor area.
Frequently asked questions
11 quick answers
How many gallons of paint do I need for a room?
A 12 ft × 12 ft room with 8 ft walls, one door and two windows needs 1.9 gallons for two coats, or 2.1 gallons with 10% extra, so buy 3. A 14 ft × 12 ft room needs 2.3 gallons, so buy 3 as well.
How do I calculate how much paint I need?
Multiply the wall area by the number of coats and divide by the coverage per gallon. Wall area is 2 × (length + width) × height, minus doors and windows. Add about 10% extra.
How many square feet does a gallon of paint cover?
A gallon typically covers about 350 to 400 square feet in one coat, according to Sherwin-Williams. Rough or textured walls and primer may need more paint, so use the number on your can.
How many gallons of paint do I need for 1,000 square feet?
One thousand square feet at 350 square feet per gallon needs 2.9 gallons for one coat or 5.7 gallons for two coats. With 10% extra that is 3.1 or 6.3 gallons.
How much paint do I need for a 12×12 room?
A 12 ft × 12 ft room with 8 ft walls has 384 sq ft of wall before openings. After one door and two windows, 334 sq ft remain, so two coats need 1.9 gallons, or 2.1 with 10% extra, which means buying 3 gallons.
How much paint do I need for a ceiling?
Ceiling area is length × width. A 12 ft × 12 ft ceiling is 144 sq ft, so two coats need 0.82 gallons, or 0.91 with 10% extra. Buy one gallon.
Do I need two coats of paint?
Two coats are standard because one rarely gives even color and coverage. One coat can be enough when repainting the same color over a clean, sound surface.
Should I subtract doors and windows?
Yes, for walls. A standard door is about 20 sq ft and a 3 ft × 5 ft window is 15 sq ft. If you also paint doors and trim, add those areas back as a separate line.
How much extra paint should I buy?
Buy about 10% extra for roller loss, cutting in and touch-ups. On a small room, rounding up to the next can usually gives more than enough.
How much does it cost to paint a room?
The paint cost is the gallons you buy times the price per gallon. At $40 a gallon, a bedroom that needs 3 gallons costs about $120 in paint, before primer, tape and supplies.
Can I use this paint calculator in liters?
Yes. Choose Metric at the top, enter meters, the coverage in m² per liter and your tin sizes, and the tool gives liters and the tins to buy.
Related calculators and worksheets
- Square footage calculator for room and floor areas
- Perimeter and area calculator for the walls of odd-shaped rooms
- Flooring calculator and concrete calculator for other DIY projects
- Percentage calculator for waste allowances
- Unit converter for feet, meters, gallons and liters
- Geometry worksheets to practice area and perimeter
Sources and further reading
- Sherwin-Williams paint calculator and FAQs for typical coverage per gallon
- EPA Renovation, Repair and Painting Program for lead-safe work in homes built before 1978
- Paint on Wikipedia for how paint is made and applied
Coverage varies by paint, surface and method. This calculator gives planning estimates, so follow the label and ask a professional about large or complex jobs.
Last updated: October 2026.