Paint Coverage Calculator
Enter your room dimensions to find out exactly how many gallons of paint you need — walls, ceiling, primer, and trim included. No guesswork, no wasted trips to the store.
Free Tool · Walls · Ceiling · Primer · Trim · Cost EstimateStandard U.S. ceilings: 8 ft (older homes), 9 ft (modern), 10 ft+ (luxury)
Standard door = 21 sq ft (3 ft × 7 ft). Excluded from wall area.
Standard window = 15 sq ft (3 ft × 5 ft). Excluded from wall area.
2 coats is standard for best coverage and durability.
Add 10% for touch-ups. Add 15–20% for textured walls or porous surfaces.
Behr ~$30–50 · Sherwin-Williams ~$45–75 · Benjamin Moore ~$50–80
Enter your room size
and hit Calculate
How Paint Coverage Is Calculated
The most common mistake DIYers make is using the manufacturer's coverage rate of 400 sq ft per gallon — a number measured under perfect lab conditions on smooth, primed surfaces. In real homes with average wall texture and painted drywall, 300–350 sq ft per gallon is a more accurate estimate. Always add a 10% waste buffer, and plan for 2 coats as the standard.
1 Gross Wall Area
Total wall surface before deductions. Multiply the room perimeter by the ceiling height. For a rectangular room, this is 2×(Length+Width)×Height.
2 Net Paintable Area
Subtract door and window areas you won't paint. Standard U.S. door = 21 sq ft (3×7 ft). Standard window = 15 sq ft (3×5 ft). Then add ceiling if painting it.
3 Gallons Needed
Divide net area by coverage rate, multiply by number of coats, then add your waste buffer. Always round up to the nearest gallon or quart at the store.
4 Total Cost
Multiply gallons needed (rounded up) by your price per gallon. Budget separately for primer, ceiling paint, and trim — these are often different products.
No matter how precise your calculation, keep a spare quart of the exact paint (same batch code if possible) for future touch-ups. Paint color can vary slightly between batches, and touch-ups done months later with a new can rarely match perfectly. Most paint retailers will store your color formula — ask them to print it on the lid.
Which Paint Finish Should You Use?
The finish (sheen level) affects both appearance and durability. Choosing the wrong finish is one of the most common DIY painting mistakes.
| Finish | Sheen | Best For | Washability |
|---|---|---|---|
| Flat / Matte | None | Ceilings, low-traffic bedrooms, hiding imperfections | Low — hard to clean, marks easily |
| Eggshell | Low | Living rooms, dining rooms, adult bedrooms | Moderate — wipes clean with mild soap |
| Satin | Medium | Kitchens, bathrooms, hallways, kids' rooms | Good — resists moisture and scrubbing |
| Semi-Gloss | High | Trim, doors, cabinets, window frames | Very good — easy to wipe down |
| High-Gloss | Mirror | Doors, furniture, accent pieces | Excellent — but shows every imperfection |