Home Paint vs Paint Coverage
Two paint calculators on this site answer closely related but different questions. The Paint Coverage Calculator is a coverage and can-count tool: it takes the walls of one room, subtracts standard-sized openings, applies surface and sheen adjustments, and tells you how many cans to buy. The Home Paint Calculator is closer to a project estimator: it lets you enter exact square footage for windows, doors, and other unpainted areas, and it has switches for ceiling and trim so the estimate covers the whole room. Both pages link to each other and describe themselves as complements — choose by whether you are counting cans for walls or planning gallons for an entire painting project.
What each calculator does
The Home Paint Calculator builds the estimate from the room’s four walls: wall area is the perimeter times wall height, unpainted areas you enter are subtracted, and optional ceiling area and a 10 percent trim allowance are added. Smooth, semi-smooth, and rough surfaces use editable coverage rates of 400, 350, and 300 square feet per gallon. The result multiplies by coats, adds 10 percent extra, and rounds up to whole gallons, reporting base gallons, gallons with the extra, total paintable area, and the recommended purchase.
The Paint Coverage Calculator focuses on wall coverage and cans. Wall area is the perimeter times height; the calculator then subtracts 20 square feet per door and 15 square feet per window automatically. Surface coverage rates are 400 square feet per gallon for smooth walls, 350 for textured walls, and 300 for new drywall, and paint type adjusts the amount further: flat paint is the baseline, eggshell divides by 0.95, and semi-gloss divides by 0.9, which increases the gallon estimate. A 10 percent allowance covers roller loading and touch-ups, and the purchase recommendation rounds up to whole cans.
Side-by-side comparison
| Feature | Home Paint Calculator | Paint Coverage Calculator |
|---|---|---|
| Scope | Whole-room project estimator | Wall coverage and can count |
| Wall area | Perimeter × height | Perimeter × height |
| Openings | Entered directly (window, door, other) | Automatic: 20 ft² per door, 15 ft² per window |
| Ceiling | Optional switch adds length × width | Not included |
| Trim | Optional switch adds 10% of wall area | Not included |
| Surface rates | Smooth 400, semi-smooth 350, rough 300 ft²/gal | Smooth 400, textured 350, new drywall 300 ft²/gal |
| Sheen | Not a separate input | Flat baseline; eggshell and semi-gloss increase amount |
| Purchase output | Whole gallons (rounded up) | Whole cans (rounded up) |
When to use which
Use the Paint Coverage Calculator for the classic weekend question: “How much wall paint should I have on hand?” It is faster because doors and windows are deducted automatically, and it is the right tool when you are only painting walls with a standard layout.
Use the Home Paint Calculator when the project goes beyond plain walls: a wall of glass, built-in cabinets, tile wainscoting, or a room where the ceiling or trim will receive the same paint. Its exact unpainted-area inputs and ceiling/trim switches make it the closer match for a full room or a rental turnover where the purchase quantity has to cover more than the wall faces.
For both, measure the room footprint first with the square footage calculator when the room is irregular, and remember that neither page estimates primer, labor, or supplies.
Where to start
- Home Paint Calculator — full room project estimate with exact openings, ceiling, and trim switches.
- Paint Coverage Calculator — wall coverage and can count with automatic door and window deductions.