Use this free paint coverage calculator to figure out exactly how much paint you need — walls, ceilings, doors, and trim included.
Estimates only. By using this calculator you agree to our Terms.
Enter multiple rooms to get a combined project total.
| Item | Area (sq ft) | Gallons/Coat | Total Gallons |
|---|
Choose a tab — Room Calculator for a single room, Single Surface for one wall or panel, or Full Project to combine multiple rooms. Enter your dimensions in feet, select the number of coats, and adjust the coverage rate if you know your specific paint's specs. Click "Calculate Paint Needed" to get your results instantly, including how many 1-gallon cans and 5-gallon buckets to purchase.
Use the door and window exclusions in the Room Calculator to avoid buying more paint than you actually need. The tool automatically subtracts those areas from your wall total.
Buying the wrong amount of paint is one of the most common — and costly — DIY mistakes. Underestimate by even 10% on a project and you risk running out mid-wall, which leads to a visible color difference when you open a new can from a different batch (even the same color can vary slightly between production runs).
On the flip side, over-buying wastes money. A gallon of premium interior paint runs $35–$70. On a whole-house repaint — say, 4 bedrooms, a living room, kitchen, and hallways — the difference between a careful calculation and a rough guess can easily be 3–5 extra gallons, costing $150+ unnecessarily.
Professionals use a coverage rate of 350–400 sq ft per gallon for smooth walls. Rough textures, bare drywall, or deep color changes often need 250–300 sq ft/gallon because porous or highly absorptive surfaces drink more paint. For best results, always apply a primer first when making dramatic color changes — this counts as a separate coat in your calculation.
The paint coverage formula is straightforward:
For example: a 15 × 12 ft room with 9 ft ceilings, 2 doors (3×6.8 ft each) and 2 windows (3×4 ft each), painted with 2 coats at 350 sq ft/gallon:
The calculator automatically rounds up to the nearest can size so you never run short.
Take a 12 × 12 ft bedroom with a 9 ft ceiling, 2 doors, and 1 window, painted with 2 coats at 350 sq ft/gallon:
If you also paint the ceiling (144 sq ft), total area becomes 523.2 sq ft, and gallons needed rise to about (523.2 × 2) ÷ 350 = 2.99 gallons — still 3 one-gallon cans, but with almost no buffer left over, so many painters round up to a fourth can for touch-ups.
Most interior latex paints cover 350–400 square feet per gallon on a smooth, previously painted surface. Rough textures, bare drywall, or highly porous surfaces typically get only 250–300 sq ft/gallon. Always check your specific paint's label — the coverage rate is always listed there.
Yes. Primer is a separate product with its own coverage rate (usually 200–300 sq ft/gallon for high-hide primers). If you're painting over a drastically different color, bare drywall, or a repaired surface, calculate primer as an additional coat. This tool handles it by letting you adjust the number of coats and coverage rate.
Yes — for interior rooms. A standard door is about 3×6.8 = 20.4 sq ft and a typical window is 3×4 = 12 sq ft. In a small room these can account for 15–20% of a wall, so subtracting them gives a meaningfully more accurate estimate. Use the exclusions section in the Room Calculator for this.
A 12×12 room with 9 ft ceilings has 432 sq ft of total wall area (2×(12+12)×9). Subtract 2 doors and 1 window (~52.8 sq ft), leaving about 379.2 sq ft. At 2 coats and 350 sq ft/gallon, that's roughly 2.17 gallons — round up and buy 3 one-gallon cans. Add the ceiling (144 sq ft) and you'll need closer to 3 gallons for 2 coats total.
For one coat on a smooth wall, you'll use roughly 1/350th of a gallon per square foot (at 350 sq ft/gallon coverage). For two coats, double that — about 1/175th of a gallon per square foot. This calculator does that math automatically based on the coverage rate you enter.
Yes, often. Dark and saturated colors, especially reds and deep blues, may need an extra coat for full, even opacity, and some manufacturers rate these paints at a slightly lower coverage rate. If you're using a bold color, consider bumping your coats setting to 3 in this calculator for a safer estimate.
Calculator by Toolwick