Paint Calculator
Gallons needed for walls, doors and windows deducted.
Enter your values
Enter the room perimeter in ft.
Enter the wall height in ft.
Enter the doors you are working with.
Enter the windows you are working with.
Enter the coats you are working with.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Paint needed
- 2.42 gallons
- Buy
- 3 gallons
- Paintable wall area
- 453 sq ft
- Primer if bare drywall
- 1.51 gallons
Quick answer
One US gallon of paint covers about 350–400 square feet per coat on primed drywall.
Gallons = wall area × coats ÷ 375
At a glance
| What it does | Gallons needed for walls, doors and windows deducted. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Room perimeter, Wall height, Doors, Windows, Coats |
| Main output | Paint needed |
| Formula | Gallons = wall area × coats ÷ 375 |
| Cost | Free — no sign-up, no download |
How to use the Paint Calculator
- 1Measure the perimeter of the room.
- 2Enter the wall height and openings.
- 3Choose how many coats you plan to apply.
Inputs explained
- Room perimeter(ft)
- Enter the room perimeter in ft.
- Wall height(ft)
- Enter the wall height in ft.
- Doors
- Enter the doors you are working with.
- Windows
- Enter the windows you are working with.
- Coats
- Enter the coats you are working with.
Worked example
Using the values the calculator loads with:
Inputs
- Room perimeter60 ft
- Wall height9 ft
- Doors2
- Windows3
- Coats2
Results
- Paint needed2.42 gallons
- Buy3 gallons
- Paintable wall area453 sq ft
- Primer if bare drywall1.51 gallons
Frequently asked questions
How much does a gallon cover?
About 375 sq ft per coat on smooth primed walls; textured or porous surfaces can drop to 250 sq ft.
Do I need primer?
Yes on bare drywall, over strong colour changes and on stained or patched areas — otherwise a self-priming paint is fine.
What do I need to enter into the Paint Calculator?
Just 5 values: room perimeter, wall height, doors, windows, coats. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Paint Calculator work out the answer?
One US gallon of paint covers about 350–400 square feet per coat on primed drywall. It applies the formula Gallons = wall area × coats ÷ 375 and shows the working so you can check each step by hand.
Is the Paint Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.