Paint Calculator
Gallons of paint and total cost for any interior or exterior job. Built for painting contractors and homeowners who want to buy the right amount the first time.
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Multiply each wall length by ceiling height. Subtract 20 sq ft per door and 15 sq ft per window.
Two coats is standard. New drywall or a color change usually needs a primer coat plus two finish coats.
Most interior latex covers 350 sq ft per gallon per coat. Rough surfaces, primer, and dark to light color changes reduce coverage.
Mid-grade interior latex is $30 to $50. Premium and exterior paint runs $50 to $90.
Your result
Always buy whole gallons. Mix all the cans together (called boxing) so the color is consistent.
- Total surface (with coats)400 sq ft × 2 coats
- 800sq ft
- Paint neededRound up to 2.5 gallons.
- 2.29gallons
- Estimated costAt $45.00 per gallon
- $135.00
Example. A 12 ft by 14 ft room with 8 ft ceilings is about 416 sq ft of wall. Two coats at 350 sq ft per gallon coverage equals 2.38 gallons. Buy 3 gallons. At $45 per gallon, the paint cost is $135.
Save this as a free estimateReal coverage per gallon
The 350 to 400 sq ft per gallon on the can is for one coat on a smooth, primed wall the same color. Real coverage usually comes in lower.
- Smooth, primed, same colorBest-case scenario.350-400 sq ft
- New drywall with primerDrywall drinks the first coat.300-350 sq ft
- Light color over dark wallPlus a primer coat first.200-300 sq ft
- Textured walls (knockdown, popcorn)250-300 sq ft
- Exterior siding (smooth)300-400 sq ft
- Exterior siding (rough cedar, stucco, brick)150-250 sq ft
If you are going from a dark wall to a light wall, do not try to skip primer. The paint store gray-tinted primer cuts your finish coats in half.
How many coats of paint do you need?
Two finish coats is the contractor default. Here is when you need more or less:
- One coat: only when the existing wall is in great shape, the color is identical, and the paint is premium grade. Rare in practice.
- Two coats: the standard. Works for almost every interior repaint where the color is changing within the same family.
- Primer plus two coats: new drywall, bare wood, any major color change, and over any surface with stains or grease.
- Three finish coats: deep reds, yellows, and oranges. The pigments in these colors are weak and need extra coverage.
Paint prices in 2026
A simple checklist before you order paint
- Measure each wall and the ceiling. Subtract doors and large windows.
- Decide on your number of coats based on the color change.
- Use 350 sq ft per gallon as the coverage estimate for interior latex unless you have a specific paint with a published rate.
- Round up to whole gallons.
- Buy all gallons of the same color at the same time and mix them together (called "boxing") so the color stays consistent across the wall.
- Save the leftover paint for touch-ups, labeled with the room and date.
Pricing the job for a client
Paint cost is the smallest line on a paint job. Labor, prep, primer, and your contractor markup are what move the number. Most painters quote $2 to $6 per square foot of wall surface for residential interior, more for ceilings and trim. Use the markup calculator to convert your raw material cost into the right selling price, and the labor cost calculator to set a defensible hourly rate.
For the bill itself, use the painting estimate template and send the final invoice with a painting invoice template. Read our guide on how to bid a paint job before you quote your next one, and check the best apps for painting contractors if you are still juggling paper estimates.
Painting over fresh drywall? Run the drywall calculator first.
How many gallons of paint do I need for a 12x12 room?
A 12 ft by 12 ft room with 8 ft ceilings has about 384 sq ft of wall surface (after subtracting one door and one window). Two coats of paint at 350 sq ft per gallon coverage equals 2.2 gallons. Round up and buy 3 gallons so you have spare for touch-ups. Add 1 gallon if the ceiling is also being painted.
How much paint do I need to paint an exterior?
For exterior siding, use 250 sq ft per gallon as the coverage estimate (lower than interior because siding is rougher and weathered). A 2,000 sq ft single-story home has about 1,200 sq ft of exterior wall surface (after windows and doors). Two coats need 9.6 gallons, so buy 10 gallons of body color plus 2 gallons of trim color.
Do I need primer before painting a wall?
Use primer when (1) the wall is new drywall or bare wood, (2) you are doing a major color change like dark to light, (3) there are stains, smoke damage, or grease, or (4) you are painting over glossy paint. Skip primer when you are repainting the same color on a clean wall that is in good shape. Tinted primer matched to your final color cuts your finish coats from three to two.
Send this paint estimate to your client
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