Use this free paint calculator to work out how many gallons or liters of paint you need for a room, after doors and windows, for any number of coats.
Home projects · feet or metersPaint Calculator
Also, each door counts as 20 sq ft and each window as 15 sq ft.
Our free paint calculator tells you exactly how much paint to buy, so you avoid both extra trips to the store and wasted cans. To begin with, enter your room’s length, width and wall height. Then add the doors, windows and number of coats. After that, the calculator shows the paint you need in gallons and quarts, or in liters.
How the Paint Calculator Works
In general, paint is sold by how much area it covers. Therefore, the calculator first finds the wall area, then divides it by the coverage on the can.
Firstly, it multiplies the room’s perimeter by the wall height.
Then it subtracts doors and windows, and adds the ceiling if you choose.
Finally, it multiplies by the coats and divides by the coverage per gallon.
The formula
Gallons = (2 × (Length + Width) × Height − openings) × coats ÷ coverage
Paint Calculator Examples
For example, here are three common rooms, so you can see how the numbers add up.
To illustrate, this bedroom has one door and two windows.
- Firstly: wall area 334 sq ft
- Then: × 2 coats ÷ 350 1.91 gal
- Also: ceiling Not painted
Similarly, this room has two doors, three windows and a painted ceiling.
- Firstly: walls and ceiling 679 sq ft
- Then: × 2 coats ÷ 400 3.4 gal
- Also: cost at $45 $157.50
In contrast, this room is measured in meters with 10 m² per liter.
- Firstly: wall area 34.2 m²
- Then: × 2 coats ÷ 10 6.84 L
- Also: cost at $12 a liter $84.00
Paint Calculator: Paint Needed by Room Size
Specifically, this table assumes 8-foot walls, one door, two windows, two coats and 350 square feet per gallon. In addition, the last column includes the ceiling.
| Room | Wall area (sq ft) | Gallons needed | Buy (walls) | Buy (with ceiling) |
|---|---|---|---|---|
| 10 × 10 ft | 270 | 1.54 | 2 gal | 2 gal + 1 qt |
| 10 × 12 ft | 302 | 1.73 | 2 gal | 2 gal + 2 qt |
| 12 × 12 ft | 334 | 1.91 | 2 gal | 3 gal |
| 12 × 14 ft | 366 | 2.09 | 2 gal + 1 qt | 3 gal + 1 qt |
| 14 × 16 ft | 430 | 2.46 | 2 gal + 2 qt | 4 gal |
| 16 × 20 ft | 526 | 3.01 | 3 gal + 1 qt | 5 gal |
| 20 × 20 ft | 590 | 3.37 | 3 gal + 2 qt | 6 gal |
How Much Does a Gallon Cover?
- Smooth drywall: for instance, about 350 to 400 square feet per gallon.
- Textured walls: similarly, about 250 to 300, because the surface soaks up more paint.
- Bare wood or new drywall: also, prime first, since unsealed surfaces absorb a lot.
How Many Coats Do You Need?
Generally, two coats give the best color and finish. However, a dark-to-light change may need a primer plus two coats. On the other hand, one coat of quality paint can be enough if the new color is close to the old one.
Primer, Ceilings and Trim
Firstly, primer covers a bit less than paint, so plan on about 300 square feet per gallon. Meanwhile, ceilings usually take a separate flat white paint, and trim often uses a semi-gloss. As a result, estimate each paint separately. Also, if your home was built before 1978, test for lead paint before sanding, as the EPA advises.
How to Use This Calculator
- To begin with, choose feet or meters and whether to include the ceiling.
- Then enter the room’s length, width and wall height.
- After that, add the number of coats, doors and windows.
- Finally, press Calculate paint to see what to buy.
More Home Project Tools
These tools also help with home jobs. Besides, you can browse all our construction calculators.
Paint Calculator FAQs
How much paint do I need for a 12×12 room?
For example, with 8-foot walls, one door and two windows, you need about 1.9 gallons for two coats. So, two gallons is usually enough for the walls.
How accurate is a paint calculator?
It is usually close, as long as you measure carefully. However, rough or porous walls and big color changes can use 10% to 20% more paint.
Do I need two coats of paint?
In most cases, yes, because two coats give even color and better durability. On the other hand, one coat may be enough when repainting a similar color with quality paint.
How many square feet does a gallon of paint cover?
Generally, most interior paint covers 350 to 400 square feet per gallon on smooth walls. Meanwhile, textured or bare surfaces may get only 250 to 300.
Should I buy quarts or gallons?
In general, gallons are much cheaper per ounce. Therefore, if you need three quarts or more, a full gallon is usually the better buy.
Does the paint calculator include doors and windows?
Yes, because it subtracts about 20 square feet for each door and 15 for each window. Also, you can set both to zero if you plan to paint them too.
Disclaimer: Overall, this calculator gives an estimate for planning only. Also, coverage depends on the paint brand, color and wall surface, so check the label and keep a little extra for touch-ups.