Estimate the paint to buy for interior walls, a ceiling, an exterior, or a primer coat. The calculator turns dimensions into paintable area, applies coats and the selected product coverage, then rounds the result to gallons and quarts.
From square feet to cans you can buy
Measure the actual surfaces, select the number of coats, and use the spread rate for the product and substrate. The calculator shows both raw gallons and a can-size recommendation so the rounding is visible.
Interior wall area uses the room perimeter multiplied by wall height.
Coverage varies by coating and surface, so use the product's published rate when available.
The calculator multiplies the same paintable area by the selected coat count.
Worked example
- The wall area is 384 sq ft.
- At 2 coats and 350 /gal, the calculation needs 2.19 gal before purchase rounding.
- The result is 2 + 1 .
Why you buy more than the can's number suggests
A coverage figure describes one coat at the stated film thickness, while the calculator multiplies the measured area by every coat you select. Texture, porosity, and preparation can also reduce spread, so the product data sheet and the actual surface should control the coverage input.
Rounding raw gallons up to cans you can buy
Coverage rate is square feet per gallon at the product's recommended film thickness. The engine retains the raw gallon result, then rounds the amount to whole gallon cans and at most one quart when that purchase covers the calculation.
Openings and extra material
Opening deductions are optional. Enter the measured combined area of the doors and windows you want to subtract instead of relying on assumed sizes. The extra-material field is also optional and has no universal default; use it only when you have a reason tied to the project or application method.
Frequently asked questions
How much paint do I need for a 12x12 room?
A 12 by 12 room with standard 8 walls has about 384 of wall. At two coats and a conservative 350 per gallon, the honest requirement is about 2.19 , which rounds up to 2 plus 1 . The can's one-coat figure would suggest only about 1.1 , so this two-coat scenario should use the two-coat amount.
How many coats of paint do I need?
Choose the coat count specified for the product and job. The calculator multiplies the measured area by that count, so one and two coats produce different quantities. Surface condition, color change, and the coating instructions should control the choice.
Do I subtract windows and doors when estimating paint?
You can. Measure the combined area of the doors and windows you want to deduct, then enter that area in More options. Leave it at zero when you prefer not to subtract openings.
Why is the coverage on the can different from what I actually get?
Published coverage assumes the product's stated film thickness and test conditions. Texture, porosity, preparation, and application can change actual spread. Use the coverage rate from your product data sheet, then lower it only when the substrate or manufacturer guidance warrants it.
How much primer do I need for new drywall?
Switch to primer mode, which uses the cited PVA drywall primer at 400 per gallon and a single coat. A 12 by 12 room with 8 walls, about 384 , needs roughly 0.96 , which rounds up to 1 . Check the product data sheet for the primer you buy because porous bare drywall and other surface conditions can change actual coverage.
How many gallons of paint do I need for a 2,000 house exterior?
Siding area, not floor area, drives the answer. As a reference point, a single-story 40 by 30 house (about 1,200 of floor area) with 10 walls and two 30 by 8 gable ends has about 1,640 of siding; at two coats and 350 per gallon that rounds up to 10 , or two 5-gallon buckets. Rough or porous siding needs more. A two-story home with 2,000 of floor area usually carries noticeably more wall area than that single-story example, so measure your actual walls in exterior mode instead of reading off the home's square footage.
Do I calculate ceiling paint separately from the walls?
Yes. A ceiling is its own quantity: area equals length times width, and it is often a different product or sheen than the walls, so it should not be folded into the wall total. A 12 by 14 ceiling is 168 , which at two coats needs about 0.96 and rounds up to 1 . Use ceiling mode, which drops the wall-height and openings fields.
How much extra paint should I buy for touch-ups and waste?
The purchase result already rounds the calculated quantity up to cans. Add a separate percentage only when your project or application method warrants more material; the calculator does not assume one universal waste rate.