Paint Calculator
Estimate how many gallons of paint you need for a room, after taking off doors and windows.
Results
| Item | Value |
|---|
Quick Answer
Multiply the room’s perimeter by the wall height, subtract doors and windows, multiply by your coats, then divide by coverage per gallon. A 12 ft by 12 ft room with 8 ft walls, 1 door and 2 windows has 334 sq ft to paint, so 2 coats at 350 sq ft per gallon takes 1.91 gallons. Buy 2 gallons.
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Table of Contents
- Paint Calculator
- Quick Answer
- Related Calculators
- How This Paint Calculator Works
- How to Use the Paint Calculator
- Core Formulas
- Worked Example
- Real-Life Examples
- Primer vs Paint
- Paint Needed by Room Size
- What Can Change How Much You Need
- Common Mistakes to Avoid
- Frequently Asked Questions
- References & Sources
How This Paint Calculator Works
This calculator finds the area of your four walls and removes doors and windows. It then multiplies by your number of coats and divides by the paint’s coverage, rounding up to whole gallons.
Quick explanation: Gallons = paintable area × coats ÷ coverage.
- Coverage: the sq ft one gallon covers. 350 is a common starting figure.
- Coats: two coats is a common choice.
- Several rooms: run each room and add the exact amounts together.
How to Use the Paint Calculator
- Measure the room’s length and width, and the wall height, in feet.
- Count the doors and windows.
- Enter the number of coats. Two is common.
- Check the coverage on the paint can, or keep 350 sq ft per gallon.
- Press Calculate to see the area, exact gallons and gallons to buy.
Core Formulas
- Wall area: 2 × (length + width) × height
- Paintable area: wall area − (doors × 20) − (windows × 15)
- Gallons: paintable area × coats ÷ coverage, rounded up
Paint makers commonly give about 350 to 400 sq ft per gallon. Some paints differ, and rough or porous surfaces can cover much less.
Worked Example
Your room is 15 ft by 12 ft, with 9 ft walls, 2 doors and 3 windows. You plan 1 coat at 400 sq ft per gallon.
- Wall area = 2 × 27 × 9 = 486 sq ft
- Paintable area = 486 − 40 − 45 = 401 sq ft
- Gallons = 401 ÷ 400 = 1.00, which rounds up to 2 gallons
With a result this close, one gallon may be enough if you are careful. Check the can before you decide.
Real-Life Examples
- An accent wall: one wall 12 ft wide and 8 ft high is 96 sq ft. Two coats need about 0.55 gallons, so 3 quarts or 1 gallon is enough.
- A bedroom: 12 ft by 14 ft with 8 ft walls, 1 door and 2 windows needs about 2.09 gallons for 2 coats. Buy 3 gallons.
- A living room with tall walls: 16 ft by 20 ft with 10 ft walls, 2 doors and 4 windows needs about 3.54 gallons for 2 coats.
- A ceiling: a 12 ft by 12 ft ceiling is 144 sq ft. One coat at 350 sq ft per gallon is about 0.41 gallons.
Primer vs Paint
- Primer: seals new drywall, bare wood and stains, and helps paint stick.
- Paint: gives the final color and finish.
- Paint and primer in one: can save a coat on walls in good condition, but may not replace a real primer on new or stained surfaces.
- Big color change: going from dark to light often needs a primer or an extra coat.
Paint Needed by Room Size
8 ft walls, 1 door, 2 windows, 2 coats and 350 sq ft per gallon.
| Room | Paintable area | Exact gallons | Gallons to buy |
|---|---|---|---|
| 10 × 10 ft | 270 sq ft | 1.54 | 2 |
| 12 × 12 ft | 334 sq ft | 1.91 | 2 |
| 12 × 14 ft | 366 sq ft | 2.09 | 3 |
| 14 × 16 ft | 430 sq ft | 2.46 | 3 |
| 16 × 20 ft | 526 sq ft | 3.01 | 4 |
| 20 × 20 ft | 590 sq ft | 3.37 | 4 |
What Can Change How Much You Need
- Surface: textured or new walls absorb more paint.
- Color change: covering a dark color often needs an extra coat or primer.
- Paint type: always check the coverage on your can.
- Touch-ups: a little left over is useful later.
Common Mistakes to Avoid
- Forgetting the second coat. One coat often looks patchy, especially with a new color.
- Using a generic coverage figure. Check the can, as some paints cover less.
- Buying exact amounts for several rooms. Add exact gallons first, then round up once.
- Skipping primer on new drywall. Bare drywall soaks up paint.
- Mixing batches mid-wall. If you need several cans, mix them together for an even color.
Frequently Asked Questions
Find the wall area, subtract doors and windows, multiply by your coats, and divide by the coverage on the can.
About 350 to 400 square feet is typical. Coverage varies by product and surface, so check the label.
With 8 ft walls, 1 door, 2 windows and 2 coats, you need about 1.91 gallons, so buy 2 gallons.
Two coats is common. You may need more when changing color or painting a porous surface.
No. It covers walls only. To estimate a ceiling, multiply length by width and divide by coverage.
A quart is a quarter of a gallon, so at 350 sq ft per gallon it covers about 87 sq ft.
A little extra is handy for touch-ups later. Rounding up to the next gallon usually covers it.
Trim usually takes much less paint than walls. A quart is often enough for the trim in one room.
References & Sources
| Source | Used For | Link |
|---|---|---|
| Sherwin-Williams, Paint calculator | Typical coverage per gallon. | https://www.sherwin-williams.com/en-us/color/color-tools/paint-calculator |
| This Old House, How much paint do I need | How to estimate paint for a room. | https://www.thisoldhouse.com/painting/how-much-paint-do-i-need |