Paint Coverage Calculator – Guide & Formulas

Estimate the amount of paint needed to complete interior or exterior paint jobs. Subtract doors and windows from your total square footage, specify the number of coats, and get instant container count recommendations.

How to Use the Paint Coverage Calculator

1. Enter the combined width and height of all walls being painted in feet.
2. Specify the number of standard doors and medium windows to subtract from the calculation.
3. Enter the target number of coats (default is 2 coats).
4. Input the paint coverage rate (the standard default is 350 sq ft per gallon).

The Formula

Variable Definitions

• W: Summed width of all walls to be painted in feet
• H: Height of the walls in feet
• N_doors: Number of doors in the painted area (average 21 sq ft subtracted per door)
• N_windows: Number of windows in the painted area (average 15 sq ft subtracted per window)
• C: Number of coats of paint to be applied
• R_coverage: The coverage capacity of a single gallon of paint (commonly 350-400 sq ft)

Painting an Average Bedroom

Find the amount of paint required for a room with four 12-foot long walls, an 8-foot ceiling, 2 doors, and 2 windows. You are planning 2 full coats of paint.

1. Step 1: Calculate total perimeter wall width: 12 × 4 = 48 feet. Total wall height is 8 feet.
2. Step 2: Calculate base gross wall area: 48 ft × 8 ft = 384 sq ft.
3. Step 3: Calculate door and window deductions: 2 doors (2 × 21 = 42 sq ft) + 2 windows (2 × 15 = 30 sq ft) = 72 sq ft to subtract.
4. Step 4: Subtract deductions to find net paintable surface: 384 - 72 = 312 sq ft.
5. Step 5: Multiply by 2 coats: 312 × 2 = 624 sq ft total coverage surface.
6. Step 6: Divide by standard coverage rate (350 sq ft/gal): 624 / 350 ≈ 1.78 gallons. Purchase two 1-gallon cans.

Frequently Asked Questions