Paint coverage calculator for a complete room estimate.
Calculate paintable area, coats, primer, standard can combinations and material cost without guessing at the store.
Typical one-coat coverage
350 ft²/gal
Walls
Ceiling
Primer
Calculator
Plan paint, primer and cans
Your paint plan will appear here
Calculate the paintable area, required volume, primer, can combination and budget.
Methodology
How the paint estimate works
For a rectangular room, wall area is perimeter multiplied by height. Doors and windows are deducted, the ceiling is optional, and the remaining area is multiplied by coats and extra allowance before dividing by product coverage.
Measure
Enter room dimensions or a known paintable area, then account for openings and ceiling.
Choose coats
Set the finish coats, primer coats and the actual coverage printed on each product.
Buy cans
The result rounds into standard package sizes so the purchase covers the calculated volume.
Formula
Paint volume = ((paintable area × coats) × (1 + extra %)) ÷ coverage per unit
FAQ
Paint calculator questions
How much paint do I need for a room?+
Add wall area and any ceiling, subtract doors and windows, multiply by the number of coats and extra allowance, then divide by the coverage shown on the paint can.
How much does one gallon of paint cover?+
Many interior products cover about 350 to 400 square feet per gallon for one coat. Rough, porous or heavily contrasting surfaces can use more.
Should I subtract windows and doors?+
Yes for a closer estimate. Small openings can sometimes offset normal waste, but larger windows and multiple doors should usually be deducted.
When should I use primer?+
Primer is commonly used for new drywall, bare or porous materials, repairs, stains and major color changes. Follow the coating manufacturer instructions.
Project guide
Use this calculator with confidence
Last reviewed: July 19, 2026
The paint calculator turns wall and ceiling dimensions into gallons or litres after opening deductions, coat count and extra allowance. Coverage is an editable product assumption rather than a promise: application method, color change, texture, porosity and surface condition all affect actual use. Use the result as a purchasing plan, then confirm coverage and primer requirements for the exact coating.
How to use it
- 1Measure the room perimeter and wall height or enter individual surfaces.
- 2Include ceilings and trim only when they will receive the same coating.
- 3Subtract meaningful doors and windows.
- 4Enter the coat count and coverage printed on the selected product.
Worked example
For 400 ft² of net wall area, two coats create 800 ft² of coating area. At 375 ft² per gallon and 10% extra, the estimate is 2.35 gallons, so the practical order is 3 gallons.
What the defaults mean
350–400 ft² per gallon
A common planning range; the product label controls.
Two coats
Useful for estimating a complete finish, but some systems differ.
Extra allowance
Covers roller loading, touch-ups and modest surface variation.
| Surface condition | Planning effect | Action |
|---|---|---|
| Smooth and similar color | near stated coverage | use label coverage |
| Porous or new drywall | higher absorption | evaluate primer |
| Rough texture or major color change | more material | increase allowance or coats |
Common measurement mistakes
- Applying one-coat coverage to a two-coat project.
- Ignoring rough, porous or repaired surfaces.
- Subtracting trim that will be painted with the same product.
- Buying exact decimal volume with no touch-up reserve.
Limits and safety
- Does not choose coating chemistry or sheen.
- Primer and specialty coatings must be calculated separately when required.
- Ventilation, lead-safe practices and surface preparation need project-specific decisions.
Continue the project
estimate primer quantity — Separate primer from finish-coat coverage.
calculate ceiling paint — Model ceilings with their own product and coat count.
estimate exterior coating — Use an exterior-specific workflow.
compare paint package cost — Turn rounded containers into a budget.