Paint planning
Paint Calculator
Estimate paint gallons from room dimensions, wall height, coats, product coverage, waste, openings, and optional cost.
Paint estimate results
- Paintable area
- 301 sq ft
- Total with coats and waste
- 662.2 sq ft
- Gallons needed
- 1.89
- Primer estimate
- 0 gallons
- Estimated cost
- Not set
Planning checklist
- Wall paint: 2 gallons
- Painter's tape: suggested
- Roller covers and drop cloth: suggested
Last reviewed: June 4, 2026
How much paint do you need?
Paint quantity depends on wall area, coats, paint coverage, surface texture, color change, and how much extra you want for touch-ups. This calculator keeps those assumptions visible instead of treating gallons as a guaranteed number.
Paint coverage formula
Gross wall area = 2 x (Length + Width) x Wall height
Paintable wall area = Gross wall area - Openings
Total with coats = Paintable area x Coats
Gallons = Total with waste / Coverage per gallon
Example calculation
A 12 ft x 10 ft room with 8 ft walls, one door, two windows, two coats, 350 sq ft per gallon coverage, and 10% extra has about 301 sq ft of paintable wall area and about 662 sq ft after coats and waste. That rounds to 2 gallons.
How to measure your room
- Measure room length, width, and wall height with one unit system.
- Count large doors and windows that should be deducted from wall area.
- Check the paint label for actual coverage before buying.
- Include ceiling area only when the ceiling is part of the same estimate.
Common paint estimating mistakes
- Forgetting the second coat.
- Using a generic coverage number instead of the product label.
- Rounding too early before coats and waste are applied.
- Ignoring porous, textured, patched, or dark-to-light surfaces.
- Buying no extra paint for touch-ups.
Paint calculator FAQ
How many square feet does a gallon of paint cover?
Many interior paints are estimated around 350 to 400 sq ft per gallon, but the product label should be the source for your final coverage value.
Should I include the ceiling?
Include the ceiling only if it will be painted with the same project estimate. Ceiling paint may have different coverage.
Should I subtract doors and windows?
Subtract large doors and windows for a cleaner planning estimate, then keep a waste factor for touch-ups and surface variation.
How much extra paint should I buy?
A small waste factor can help with touch-ups, roller loading, texture, and small measuring differences. Product and project conditions still matter.
Can this calculator estimate primer?
Yes, the optional primer estimate uses the same coverage value as a planning shortcut. Primer coverage can differ, so check the label.