Paint Calculator
Calculate how many gallons of paint you need for a room, including walls and optional ceiling.
How to Calculate Paint Coverage
The formula is straightforward: Gallons = (Wall Area × Coats) ÷ Coverage Rate. Wall area is the total paintable surface — the perimeter of the room multiplied by the ceiling height, minus deductions for doors and windows.
Most interior latex paints cover 350–400 sq ft per gallon on a primed surface. If your walls are textured, unpainted drywall, or a very different color from the new paint, use a lower coverage rate (300 sq ft/gallon) to avoid running short.
Paint Coverage Reference
| Surface Type | Sq Ft / Gallon |
|---|---|
| Smooth primed drywall | 350–400 |
| Previously painted smooth wall | 350–400 |
| Textured wall / orange peel | 300–350 |
| Unpainted / bare drywall | 250–300 |
| Rough masonry / brick | 150–200 |
| Exterior wood siding | 300–400 |
Frequently Asked Questions
How many square feet does a gallon of paint cover?
A gallon of paint typically covers 350–400 square feet with one coat on a smooth, primed surface. Rough or porous surfaces absorb more paint and may only yield 250–300 sq ft per gallon. This calculator uses 350 sq ft/gallon as the default, which you can adjust.
How many coats of paint do I need?
Most painting jobs require 2 coats for full, even coverage — especially when changing colors or painting over dark colors. A single coat may be sufficient for touch-ups or when using paint-and-primer combinations on already-painted surfaces.
Do I need to paint the ceiling?
Ceilings are often painted separately from walls and typically require fewer coats (1–2) since they aren't touched or scuffed. If you're painting a full room, factor in the ceiling as a separate project. This calculator includes an optional ceiling toggle.
Should I subtract doors and windows from my paint calculation?
Yes — it's standard practice to subtract standard door and window areas from total wall area. A typical interior door is about 21 sq ft (3×7 ft) and a window is about 15 sq ft (3×5 ft). Subtracting these prevents over-buying, though many painters still round up slightly.
How do I calculate paint for an oddly shaped room?
For L-shaped or irregular rooms, break the room into rectangular sections and calculate each separately. Add all the wall areas together, then subtract doors and windows. Alternatively, measure all four wall perimeters and multiply by ceiling height for a quick estimate.