Nothing is more frustrating than running out of paint halfway through a room — or ending up with five gallons of unused paint. Here’s how to calculate exactly what you need.
The Basic Formula
To estimate paint, you need to know the surface area and the paint’s coverage rate. Most paint covers about 350-400 square feet per gallon.
Wall area: Measure the perimeter of the room and multiply by the ceiling height. Then subtract windows and doors.
How Our Paint Calculator Works
Our paint calculator handles all the details:
- Walls — Calculates wall area minus windows and doors
- Ceiling — Separate calculation for ceiling paint
- Trim — Baseboards, crown molding, and door frames
- Coats — Accounts for number of coats (2 is standard for most colors)
Measuring Your Room
- Measure the length of each wall and add them together (perimeter)
- Multiply perimeter by ceiling height to get total wall area
- Measure window height and width, multiply for each window
- Measure door height and width, multiply for each door
- Subtract total window and door area from wall area
Example: 12x14 ft room with 8 ft ceilings, two windows (3x4 ft each), one door (3x7 ft):
- Perimeter: (12+14) x 2 = 52 ft
- Wall area: 52 x 8 = 416 sq ft
- Windows: 2 x (3 x 4) = 24 sq ft
- Door: 3 x 7 = 21 sq ft
- Net wall area: 416 - 24 - 21 = 371 sq ft
- Gallons needed (2 coats): 371 x 2 / 350 = 2.1 gallons
Paint Finishes Explained
| Finish | Best For | Characteristics |
|---|---|---|
| Flat/Matte | Ceilings, low-traffic areas | Hides imperfections, harder to clean |
| Eggshell | Living rooms, bedrooms | Slight sheen, easy to clean |
| Satin | Kitchens, bathrooms, hallways | Durable, washable |
| Semi-gloss | Trim, doors, cabinets | Very durable, easy to clean |
| Gloss | High-traffic trim, furniture | High shine, most durable |
Tips for Buying Paint
- Buy all paint at once — Different batches can have slight color variations
- Round up — Buy a full gallon rather than getting close to running out
- Save leftover paint — Label the can with the room and date for touch-ups
- Consider primer — New drywall, dark colors, and stained walls need primer first
- Quality matters — Better paint covers better and lasts longer
Common Paint Coverage Rates
| Surface | Coverage Per Gallon |
|---|---|
| Smooth drywall | 400 sq ft |
| Textured drywall | 300-350 sq ft |
| Previously painted | 350-400 sq ft |
| Brick or rough surface | 200-300 sq ft |
| Ceiling paint | 350-400 sq ft |
FAQ
How much paint do I need for one wall?
Measure the wall’s height and width, multiply for square footage, subtract windows and doors, then divide by 350 (average coverage per gallon). Our paint calculator does this instantly.
Is primer included in the paint calculator?
No — primer is calculated separately. Most rooms need one coat of primer followed by two coats of paint. Primer coverage is typically 250-300 sq ft per gallon.
How much paint for a 12x12 room?
A standard 12x12 room with 8-foot ceilings needs about 1.5 gallons of paint for two coats on walls, plus 1 gallon for the ceiling and 0.5 gallons for trim. Use our calculator for exact amounts.
Should I buy all paint at once?
Yes — buy all your paint at once to ensure color consistency across batches. Different production batches can have slight color variations.
Summary
Accurate paint estimation saves money and trips to the hardware store. Use our paint calculator to calculate exact gallons for walls, ceilings, and trim with any number of coats.