This Paint Calculator estimates how much wall space you need to cover and how many gallons of paint will finish the job. Homeowners planning a weekend refresh, contractors quoting a repaint, and property managers budgeting unit turnovers all use it before buying a single can.
Results appear as Total area, Paint needed, and Estimated cost. Pick Internal painting or External painting, and swap between the Imperial (feet, inches, lbs) and Metric (mm, cm, m, kg) unit systems whenever your measurements demand it, keeping labels and receipts consistent.
How the paint estimate is worked out
The estimate leans on the guide coat rule: one gallon of wall paint covers roughly 350 to 400 square feet per coat. Total coverage demand equals paintable area multiplied by the number of coats, and gallons needed equals that demand divided by the coverage rate.
Worked example: a bedroom with 1,000 square feet of wall, less two doors of 21 square feet and two windows of 15 square feet, leaves 928 square feet. Two coats require 1,856 square feet of coverage, and 1,856 divided by 375 gives 4.95, so 5 gallons is the right purchase.
Using the inputs and avoiding surprises
Enter each wall’s length and height, then subtract door and window openings so you never pay for paint that goes nowhere. Set your number of coats deliberately, because forgetting the second coat is the most common reason estimates fall short on the job.
Textured or fresh drywall drinks more product, so lean toward the 350 square foot end of the coverage range there. Always round up to whole gallons, bank a little extra for touch ups, and expect deep colors to demand a third coat for a uniform finish.
Frequently Asked Questions
How much area does one gallon of paint cover?
A gallon of interior wall paint typically covers 350 to 400 square feet with a single coat. Rough or primed surfaces reduce that toward 350, while smooth sealed walls can reach 400.
Should doors and windows be subtracted?
Yes, subtract every opening because paint is not applied there. A standard door removes about 21 square feet and a typical window removes roughly 15 square feet from the wall total.
How many coats should I plan for?
Plan on two coats for most color changes, which doubles the coverage needed. A 900 square foot room therefore requires 1,800 square feet of coverage, or about 5 gallons at 375 square feet per gallon.
Do I need primer with new drywall?
New drywall absorbs paint quickly, so a primer coat seals it first. Count the primer as one coat; 400 square feet of fresh drywall then needs about 1.1 gallons of primer, so buy a full gallon and a quart.
Does the calculator include ceiling areas?
Most wall based estimates exclude ceilings, so measure them separately and add the area. A 12 by 12 foot ceiling adds 144 square feet, another half gallon per coat at a 375 square foot rate.