Paint Calculator
A quick way to turn room dimensions into paintable wall area and gallons to buy, after doors and windows come out. It helps painting contractors write supply lists and keeps homeowners from buying too much or too little.
Free, no sign-up. Runs in your browser; nothing you type is stored unless you choose to email yourself the results.
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Email me these results. We'll send your numbers, plus how to turn this calculator into a lead magnet on your own website.
Three steps, about a minute
Step 1
Enter Room length, Room width and Wall height in feet, measured at the floor.
Step 2
Count the Doors and Windows, then set how many Coats you plan to roll.
Step 3
Enter Coverage per gallon from the paint can label to get Gallons to buy.
How the paint calculator works
Wall area is the room's perimeter times its height: 2 × (length + width) × height. The tool subtracts about 21 sq ft for each door and 15 sq ft for each window, and it never lets the area fall below zero. Gallons needed is paintable area × coats ÷ coverage per gallon, and Gallons to buy rounds that up to whole cans. A 14 × 12 ft room with 8 ft walls, one door and two windows has 365 sq ft of paintable wall, so two coats at 350 sq ft per gallon take about 2.1 gallons, and you buy 3. Ceilings, trim and the doors themselves are not included, so figure those separately. New drywall, stucco and bare wood soak up more paint, so lower the coverage number or plan a primer coat first.
| Room length | 14 ft |
|---|---|
| Room width | 12 ft |
| Wall height | 8 ft |
| Doors | 1 |
| Windows | 2 |
| Coats | 2 |
| Coverage per gallon | 350 sq ft |
| Paintable wall area | 365 sq ft |
|---|---|
| Gallons needed | 2.1 |
| Gallons to buy | 3 |
Subtracts about 21 sq ft per door and 15 sq ft per window.
Using the numbers like a pro: tips for painters
Box your paint: pour every can of one color into a 5-gallon bucket and mix before you start. Slight differences between cans disappear, and the walls look even corner to corner.
Price by wall area and prep, not by gallons. Patching, sanding, masking, cutting in and cleanup drive your hours, and a gallon count alone undersells the work.
Leave a labeled container of each color with the homeowner and write the color name and code on the invoice. Touch-ups get easier, and they remember who to call.
Put a calculator like this on your own website
Homeowners planning a repaint often price the paint before they price the labor. A calculator on your site that shows gallons, then offers a full quote with prep and labor, catches them at that moment. Ask for room count and preferred start date in the form so you can prioritize callbacks and fill gaps in your schedule.
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Paint Calculator questions
How much paint do I need for a 12x12 room?
With 8 ft walls, a 12 by 12 ft room has 384 sq ft of wall. Subtract about 21 sq ft per door and 15 sq ft per window. With one door and two windows that leaves 333 sq ft, so two coats at 350 sq ft per gallon take about 1.9 gallons. Buy 2.
How many square feet does a gallon of paint cover?
Most interior paint labels list coverage somewhere in the 250 to 400 sq ft per gallon range for smooth, primed walls. Rough, porous or unprimed surfaces get less. This calculator defaults to 350 sq ft per gallon, but the coverage printed on your can is the number to use.
Do I need two coats of paint?
Usually. Two coats give even color and hold up better, especially with a big color change or a light shade over a dark one. A single coat can work when repainting the same color over walls in good shape. Fresh drywall needs a coat of primer first.
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