Paint Coverage Calculator
Use this paint coverage calculator to estimate gallons or liters for a room or wall project. Enter room dimensions or total area, subtract doors and windows, choose coats and waste, and get an instant paint quantity estimate.
Height of the walls you plan to paint.
Default interior door opening is about 21 sq ft.
Default medium window opening is about 15 sq ft.
Most interior walls need two coats for even coverage.
Check your paint can label; 350 sq ft per gallon is a common interior estimate.
Adds extra paint for touch-ups, uneven surfaces, and roller tray loss.
- Total wall area
- 352 sq ft
- Adjusted paintable area
- 352 sq ft
- Total coverage required
- 704 sq ft
- Estimated paint needed
- 2.21 gal
- Buying guidance
- Buy 2 gallons + 1 quart
How this estimate is calculated
Estimate = (paintable area − openings) × coats ÷ coverage rate × (1 + waste%). Results update instantly as you edit inputs.
How to calculate paint needed
Start with the total paintable wall area. In room mode, the calculator uses 2 × (length + width) × height, which covers all four walls without the ceiling.
Subtract doors, windows, or a custom opening area so you do not overbuy for unpainted surfaces.
Multiply the adjusted area by the number of coats, divide by your paint can coverage rate, then add your waste percentage for touch-ups and uneven absorption.
Paint coverage assumptions and why rates vary
Most interior latex paints list coverage around 350–400 square feet per gallon on smooth, primed drywall. Rough or porous surfaces, dark color changes, and spraying often need a lower coverage assumption.
This tool keeps coverage editable so you can match the label on the can you plan to buy. When in doubt, use the lower number on the label to avoid a mid-project store run.
How to subtract doors and windows
Count mode uses editable default opening sizes: about 21 sq ft per standard interior door and 15 sq ft per medium window in imperial units, with metric equivalents provided automatically.
If you measured openings yourself, switch to custom area mode and enter the combined square footage or square meters to subtract.
Gallons vs liters conversion guidance
Imperial results show gallons with buying guidance rounded up to the nearest quarter gallon, including a gallons-plus-quarts breakdown when helpful.
Metric results show liters rounded to a practical tenth for the estimate and suggest whole-liter purchase quantities. One U.S. gallon is about 3.785 liters if you are comparing labels across regions.
Frequently Asked Questions
How much paint do I need for a room?
Measure the room or enter total wall area, subtract doors and windows, choose your coat count, and divide by the coverage rate on your paint can. This calculator applies those steps instantly and adds a waste allowance so you buy enough for touch-ups.
How much area does one gallon of paint cover?
Many interior paints cover about 350–400 square feet per gallon on smooth, primed walls with one coat. Coverage drops on textured, porous, or unprimed surfaces, so adjust the coverage field to match your product label.
How many coats of paint should I plan for?
Two coats is the default for most interior repaints because it improves opacity and durability. One coat may work for similar-color refreshes, while dramatic color changes often need two coats or a dedicated primer coat.
Why add a waste or overage percentage?
Waste accounts for roller tray residue, brush cleanup, cutting-in loss, and uneven surfaces that absorb more paint. A 10% allowance is a practical starting point for DIY room projects.
Does textured or uneven drywall change the estimate?
Yes. Textured, popcorn, brick, or heavily patched walls usually need more paint than smooth drywall. Lower the coverage rate or raise the waste percentage in this calculator to reflect those surfaces.
Can I enter total wall area instead of room dimensions?
Yes. Switch to direct area mode when you already know the paintable square footage or square meters from a floor plan, takeoff sheet, or manual measurement.