Loan Paint Coverage Calculator
Enter your room's dimensions, subtract doors and windows, and get exactly how many gallons of paint to buy — no more guessing at the store.
| Total wall area | 0 sq ft |
| Minus doors & windows | 0 sq ft |
| Paintable area (with coats) | 0 sq ft |
| Coverage rate used | 350 sq ft / gal |
How it works
Wall area is 2 × (length + width) × height, minus 21 sq ft per door and 15 sq ft per window, multiplied by the number of coats. At the standard coverage of 350 sq ft per gallon, the result is rounded up — you can't buy a partial gallon.
Formula & worked example
Formula: Wall area = 2 × (length + width) × ceiling height. Subtract 21 sq ft per door and 15 sq ft per window, multiply by the number of coats, then divide by 350 sq ft per gallon and round up.
Worked example: A 12 ft × 10 ft room with 8 ft walls has 352 sq ft of wall. Two doors and two windows remove 72 sq ft, leaving 280 sq ft; two coats mean 560 sq ft to cover, so 560 ÷ 350 rounds up to 2 gallons.
When to use this
- You are repainting a bedroom and want the gallon count settled before the color is even final.
- A painter's estimate includes paint and you want to know how many gallons the room honestly takes.
- You are doing a rental turnover — same color, several rooms — and need a total buy in one batch.
- The walls are taller than the usual 8 ft and every rough guide you have found quietly assumed they were not.
How to use it, step by step
- Enter the room length, width and wall height in feet.
- Count the doors and windows in the room — they come off the paintable area.
- Choose the number of coats you will actually apply.
- Click Calculate paint and read the wall area, the deduction and the gallons together.
- Buy the rounded-up gallons in one batch so the color matches across coats.
What the inputs mean
| Input | What it is | Typical values |
|---|---|---|
| Room length and width | The floor dimensions that set the wall perimeter | 12 by 15 ft is the page's starting example |
| Wall height | Floor-to-ceiling height the perimeter is multiplied by | 8 ft standard, 9 ft in many newer rooms |
| Doors | Count of doors, each deducting about 21 sq ft | 1 or 2 in most bedrooms |
| Windows | Count of windows, each deducting about 15 sq ft | 2 is the page default |
| Coats | How many coats the job gets | 1, 2 or 3 — 2 is the usual repaint |
Another worked example
A 14 by 11 ft room with 9 ft walls has 450 sq ft of wall. One door and three windows remove 66 sq ft, leaving 384 sq ft to paint; two coats make 768 sq ft of coverage. At 350 sq ft per gallon that is 3 gallons to buy — the tall walls are what push this ordinary-sized bedroom past the 2-gallon answer most people walk in expecting.
Frequently asked questions
How many square feet does a gallon of paint cover?
Most interior latex paints cover about 350 square feet per gallon per coat. Primer and cheap paints may cover less.
Should I paint one coat or two?
Two coats give even color, better durability, and truer coverage of the old color. One coat is fine for a refresh in the same color.
Do I need primer too?
On bare drywall, stains, or dramatic color changes — yes. Over existing paint in good shape, a quality paint-and-primer is usually enough.
Does this include painting the ceiling?
No — the formula is walls only: perimeter times height, minus doors and windows. If the ceiling is getting paint too, work it out separately as length times width divided by 350 per gallon per coat, and add that to the wall gallons. Ceiling paint is also a different, flatter product, so it should be its own purchase line anyway.
What about trim, baseboards and the inside of closets?
They are not in this count. The door deduction assumes the door slab itself is not being painted with wall paint, and trim normally gets a separate semi-gloss product in much smaller quantities. Closet interiors do get wall paint in many repaints — if yours are, measure the closet walls and run them as their own small room rather than ignoring them.
Do textured walls or a dark color underneath change the count?
They can. Heavy texture soaks up paint in its valleys, and covering a dark color with a light one often needs an extra coat to stop the old shade grinning through — the calculator's note flags both cases. If either applies, price the job at the next coat up and treat any leftover as your touch-up supply rather than discovering the shortfall mid-wall.
🛠️ Planning a bigger project?
Estimate deck lumber with our deck material estimator, or compare paint prices per ounce with the unit price calculator.