Paint Coverage Calculator
A free paint coverage calculator that tells you how many gallons of paint you actually need for a room. Accounts for surface texture, finish, coats, and the doors and windows you do not paint over.
Room Dimensions
Surface & Coats
Cost (optional)
You need
How to use this paint coverage calculator
The paint coverage calculator works for any single room. The math runs in your browser the moment you change an input — no button to press, no signup. Use the toggle at the top to switch between Imperial (feet, gallons) and Metric (meters, liters) — the calculator handles the unit conversion internally.
- Measure the room in feet (or meters). You need length, width, and ceiling height. Most US ceilings are 8 feet (2.4 m); older homes and modern luxury builds run 9 or 10 feet (2.7-3.0 m).
- Count doors and windows in the room. The calculator subtracts about 20 sq ft (1.9 m²) per door and 15 sq ft (1.4 m²) per window — close to the standard sizes (32"×80" door, 36"×60" window). For unusually large openings, add to the "other excluded" field.
- Pick your surface type. Smooth drywall is the default. If your walls have orange peel, knockdown, or popcorn texture, the calculator uses lower per-gallon (per-liter) coverage — textured surfaces have more actual surface area to cover.
- Set the number of coats. Two coats is standard. One coat works for touch-ups in the same color. Three coats is realistic if you are painting a light color over a dark one, or vice versa. See our coats of paint decision guide for the full matrix by scenario.
- Turn on primer if you are painting new drywall, covering a dark color, or sealing a stained or oily surface. The calculator estimates primer separately at 250 sq ft per gallon (6.1 m² per liter).
- Toggle cost estimation if you want a rough material total. The default price of $40 per gallon ($11 per liter) matches mid-range US paint in 2026. Premium paints run $50-70 per gallon ($13-19 per liter); budget paints $15-25 per gallon ($4-7 per liter).
Why "400 sq ft per gallon" usually misleads
Most paint cans state coverage of 350 to 400 square feet per gallon (8.6 to 9.8 square meters per liter). Sherwin-Williams publishes 350-400 sq ft/gal (8.6-9.8 m²/L) as their standard. Benjamin Moore uses 400 sq ft per gallon (about 9.8 m² per liter) as the typical figure for their flagship lines. Those numbers are accurate — under ideal conditions.
"Ideal conditions" means smooth, properly primed drywall, applied by a professional, in good environmental conditions, in a single coat. Real-world walls have texture, real-world painting takes two coats, and real-world rooms have corners, trim, and cut-ins that consume more paint than the open wall surface suggests. The 400 sq ft (9.8 m² per liter) figure assumes none of that.
How coverage really changes by surface
Textured walls have more actual surface area than smooth walls of the same dimensions. Industry estimates put the coverage rates roughly as follows:
| Surface | Per gallon | Per liter |
|---|---|---|
| Smooth drywall | 350 sq ft | 8.6 m² |
| Orange peel texture | 300 sq ft | 7.4 m² |
| Knockdown texture | 275 sq ft | 6.7 m² |
| Popcorn texture (ceilings) | 225 sq ft | 5.5 m² |
| New unprimed drywall | 250 sq ft | 6.1 m² |
| Stucco or brick | 175 sq ft | 4.3 m² |
The drop is mechanical. A popcorn ceiling has roughly 1.5× the actual surface area of a smooth ceiling of the same flat dimensions — every popcorn bump is a bit of extra surface that needs to be coated. The paint can label can't predict your wall texture, so it states the ideal-case number.
That is also why the industry standard adds a 10% buffer to any paint calculation. Professional painters typically add 10-15% for waste, roller absorption, cut-in overlap, and touch-ups. This calculator applies 10% by default — appropriate for brush and roller jobs with reasonably geometric rooms.
The math behind the result
Here is the exact calculation. Nothing is hidden. Numbers shown in both imperial and metric:
- Wall area = 2 × (length + width) × ceiling height. For a 12×10 ft (3.7×3.0 m) room with 8 ft (2.4 m) ceilings, that is 2 × 22 × 8 = 352 sq ft (about 32.7 m²) of wall.
- Ceiling area (if included) = length × width. For 12×10 ft (3.7×3.0 m), that adds 120 sq ft (11.1 m²).
- Subtractions = (doors × 20 sq ft / 1.9 m²) + (windows × 15 sq ft / 1.4 m²) + other excluded area. One door and one window = 35 sq ft (3.3 m²).
- Paintable area = wall area + (optional ceiling) − subtractions. The example becomes 352 − 35 = 317 sq ft (29.4 m²) of paintable wall.
- Total surface to coat = paintable area × number of coats. With 2 coats, the 317 sq ft (29.4 m²) becomes 634 sq ft (58.9 m²) total.
- Raw paint = total surface ÷ surface coverage rate. At 350 sq ft/gal (8.6 m²/L) for smooth drywall, 634 ÷ 350 = 1.81 gallons (or 58.9 ÷ 8.6 = 6.85 liters).
- With 10% buffer = raw × 1.10 = 1.99 gallons (7.54 liters).
- Final answer = round up = 2 gallons (or 8 liters).
Primer math runs separately with a 250 sq ft per gallon (6.1 m² per liter) rate and the same 10% buffer. Cost simply multiplies the gallon (or liter) count by your per-gallon (per-liter) price.
Frequently asked questions
How does this paint coverage calculator work?
Enter your room dimensions, choose the surface type and finish, and set the number of coats. The calculator multiplies wall area by coats, divides by the per-gallon coverage rate for your surface (350 sq ft for smooth drywall, less for textured surfaces), adds a 10% buffer for waste and touch-ups, and rounds up to whole gallons. Doors and windows are subtracted automatically with reasonable defaults.
Why does this say I need more paint than the can label promises?
Paint can labels typically state 350-400 sq ft per gallon under ideal conditions — smooth drywall, properly primed, applied by a pro. Real walls have texture, need two coats, and have cut-ins and edges that consume more paint. Industry standard adds a 10-15% buffer. This calculator uses conservative coverage rates and a 10% buffer for a realistic estimate, not the manufacturer's best case.
Does this calculator save my inputs or send data anywhere?
No. Everything runs entirely in your browser. Room dimensions, surface choices, and cost estimates are never sent to any server. Nothing is stored after you close the tab. You can verify this in your browser's developer tools network tab.
Should I buy extra paint just in case?
Yes. The calculator already adds a 10% buffer, which is industry standard for brush and roller application. For complex rooms with many corners, trim, or cut-ins, professionals often add 15-20% instead. Keeping a small amount of leftover paint also makes future touch-ups much easier — the color is hard to match precisely once the original can is gone.
Does the gallon count include primer?
No. Paint and primer are calculated separately. Turn on "Need primer" if you are painting new drywall, covering a dark color with a light one, or sealing a stained or oily surface. Primer coverage is about 250 sq ft per gallon — less than paint because primer needs to soak into porous surfaces.
What if I am only painting one accent wall?
Set the room length and width to match the dimensions of the wall you are painting, and set the other dimension to a very small number (0.1 or similar). The calculator computes wall perimeter times ceiling height. A simpler workaround for a single wall: take the wall's width × ceiling height directly, multiply by your coats, divide by 350 (for smooth drywall), and add 10%.
What ceiling height should I use?
Most US homes have 8-foot ceilings, which is the calculator's default. Mid-century and ranch homes often have 8 ft. Newer construction frequently runs 9 ft on the main floor. Vaulted ceilings, lofts, and luxury builds can go 10-12 ft or higher. Measure if you are unsure — a 1-foot difference adds about 10% to the wall area in a typical room.
Why is popcorn ceiling coverage so much lower?
Popcorn texture has visible bumps and ridges. Each bump is a small piece of additional surface that has to be painted. The total surface area of a popcorn ceiling is roughly 1.5× the flat dimensions of the room. The calculator uses 225 sq ft per gallon (5.5 m² per liter) for popcorn versus 350 sq ft per gallon (8.6 m² per liter) for smooth — about a 36% reduction.
Does this calculator work in meters and liters?
Yes. Use the Imperial / Metric toggle at the top of the calculator. Imperial mode uses feet, square feet, and US gallons (1 US gal = 3.785 liters). Metric mode uses meters, square meters, and liters. The same math runs internally — only the input labels and output units change. Coverage rates are equivalent: 350 sq ft per gallon equals 8.6 square meters per liter.