Paint Calculator
Calculate exactly how many gallons of paint you need for any room. Accounts for doors, windows, and number of coats.
How to Calculate Paint for a Room
To estimate paint, calculate the total wall area by adding up the length of all walls and multiplying by the ceiling height. Then subtract the area of doors (about 21 sq ft each) and windows (about 15 sq ft each). Divide the paintable area by the paint's coverage rate (typically 350 sq ft per gallon) and multiply by the number of coats.
Paint Coverage by Type
| Paint Finish | Coverage per Gallon | Best For |
|---|---|---|
| Flat / Matte | 350–400 sq ft | Ceilings, low-traffic rooms |
| Eggshell | 350–400 sq ft | Living rooms, bedrooms |
| Satin | 350–400 sq ft | Kitchens, hallways, kids' rooms |
| Semi-Gloss | 300–350 sq ft | Bathrooms, trim, doors |
| Gloss | 300–350 sq ft | Trim, cabinets, furniture |
Tips for Accurate Paint Estimates
- Always round up — it's better to have a little extra than to run short mid-project.
- Dark colors over light walls (or vice versa) may need an extra coat beyond the standard two.
- Textured walls absorb more paint and may require 10–20% more than smooth surfaces.
- Keep at least half a gallon for future touch-ups, especially in high-traffic areas.
- Most paint stores can color-match if you need more later, but batch colors can vary slightly.
Do I Need Primer?
Primer is recommended when painting over new drywall, covering dark colors with a lighter shade, painting over stains or patches, or switching between paint types (e.g., oil to latex). Many modern paints include built-in primer, but for best results on challenging surfaces, a separate primer coat will give you better coverage and adhesion.
Frequently Asked Questions
A 12x12 room with 8-foot ceilings has about 384 sq ft of wall area. After subtracting a standard door (21 sq ft) and two windows (30 sq ft), you have roughly 333 sq ft of paintable surface. At 350 sq ft per gallon, one gallon covers a single coat. For the recommended two coats, buy 2 gallons.
One gallon of standard interior latex paint covers approximately 350-400 square feet on smooth surfaces with one coat. Semi-gloss and gloss finishes cover slightly less, around 300-350 sq ft per gallon. Textured or porous surfaces may reduce coverage by 10-20%.
Primer is recommended when painting over new drywall, switching from a dark color to a light one, covering stains or patches, or changing paint types (oil-based to latex). Many modern paints include built-in primer, but a separate primer coat gives better coverage and adhesion on challenging surfaces.
Two coats is the standard recommendation for most interior painting projects. You may need three coats when covering a dark color with a much lighter one, or when using certain red and yellow pigments that have poor hiding power. A single coat may work when repainting the same color or using high-quality paint-and-primer-in-one products.
For a DIY paint job on a standard 12x12 room, expect to spend $50-$100 on paint (2 gallons of mid-range latex), plus $20-$40 on supplies like rollers, brushes, tape, and drop cloths. Professional painters typically charge $300-$700 per room depending on size, prep work, and your location.