Gallons needed--
1-gallon cans--
Paint Calculator for Walls and Rooms
Use this paint calculator to estimate gallons and cans before heading to the store.
Updated May 2026No signup requiredBuilt for mobile
Formula or method
Gallons = area x coats / coverage.
Add a waste or reserve percentage for touchups and surface variation.
Worked examples
Bedroom repaint
A room with 500 square feet of paintable wall area, two coats, and 350 square feet per gallon needs about 2.9 gallons before reserve, so three gallons is the practical starting point.
Color change reserve
If the same room is changing from a dark color to a light color, increase the reserve or plan primer because real coverage can be lower than the label average.
Practical use cases
- Estimating gallons before visiting the paint counter.
- Comparing one-coat touchups with full two-coat repainting.
- Planning primer, wall paint, ceiling paint, and trim paint separately.
- Checking whether a near-boundary estimate needs another can.
- Budgeting paint for rental turnover, bedrooms, garages, and small remodels.
Common mistakes
- Using label coverage without considering texture, color change, or porous drywall.
- Forgetting closets, alcoves, trim-heavy areas, ceilings, or second coats.
- Subtracting every small opening even though cutting in still uses paint.
- Buying no extra for touchups from the same batch.
FAQ
Paint Calculator questions
How accurate is this calculator?
It is a planning estimate based on your area, coverage, coats, and reserve. Surface texture, color change, primer, application method, and product coverage can change the final amount.
Why do results vary?
Coverage changes with wall texture, repairs, roller type, paint quality, primer, humidity, and how much cutting in is required.
Should I round up?
Round conservatively when running short would interrupt a project, backup, stream, trip, or outage plan.
What should I do next?
Use the result card and checklist, then compare related calculators or guides before making a final decision.
Does this replace official documentation?
No. Use manufacturer documentation, platform guidance, or professional advice for critical decisions.
How to use this estimate
The paint calculator estimates gallons from wall area, coats, openings, coverage rate, and reserve. It helps plan interior rooms, garages, sheds, trim-heavy spaces, and exterior surfaces before buying paint, primer, rollers, tape, and drop cloths.
Inputs that matter most
- Wall length, height, or total square footage.
- Doors, windows, cabinets, or areas that should be subtracted.
- Number of coats and whether primer is separate from finish paint.
- Coverage per gallon from the actual product label.
Formula and method
Paint needed = adjusted paintable area x number of coats, divided by coverage per gallon. Add reserve for texture, color changes, touch-ups, roller loss, and future repairs, then round to the nearest practical can size.
A result near a can boundary deserves caution. If the estimate is 1.95 gallons, buying exactly two gallons leaves almost no room for texture, spills, color changes, or later touch-ups.
Worked example
Example: a room has 420 square feet of wall area after subtracting windows and doors. Two coats create 840 square feet of coverage demand. If the paint covers 350 square feet per gallon, the job needs 2.4 gallons before reserve. Rounding to three gallons gives enough for normal application and touch-up.
Common planning mistakes
- Using advertised coverage without checking the product label and surface condition.
- Forgetting primer, second coats, trim, closets, ceilings, or textured walls.
- Subtracting openings too aggressively when small areas still need cutting in.
- Buying paint in separate batches that may not match perfectly.
Safety and disclaimer note
Paint estimates are planning aids, not professional contractor advice. Follow product labels, ventilation instructions, surface-preparation guidance, lead-paint rules for older homes, ladder safety, and local disposal requirements; consult a qualified professional for hazardous surfaces or large projects.
FAQ
Practical questions
Should I subtract windows and doors?
Yes for larger openings, but do not over-subtract small openings because cutting in and waste still use paint.
How many coats should I enter?
Use the number of finish coats you expect. Major color changes, stains, and porous surfaces may also need primer.
Why does textured wall coverage differ?
Texture increases surface area and roller loss, so real coverage can be lower than the label average.
Should I buy extra paint?
A modest reserve helps with touch-ups, spills, and future repairs, especially if color matching may be difficult later.
Can this estimate include ceilings?
Use a separate area or calculator pass for ceilings because product, sheen, and coverage may differ from walls.