Calculate exactly how much paint you need — walls, ceilings, doors, and trim.
Enter multiple rooms or surfaces 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.
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 756 sq ft of total wall area (2×(12+12)×9). Subtract 2 doors and 1 window (~55 sq ft), leaving ~701 sq ft. At 2 coats and 350 sq ft/gallon, you'd need about 4 gallons. With ceiling included, add 144 sq ft — pushing total to roughly 4.8 gallons, so buy 5.