Search calculators, converters, tools... ⌘K

Paint Calculator

Calculate paint gallons and liters needed for interior or exterior walls, accounting for doors, windows, and coats.

Length of the room in feet.
Width of the room in feet.
Standard ceiling height is 8 to 9 feet.
Subtracted as ~21 sq ft each.
Subtracted as ~15 sq ft each.
Most interior projects require 2 coats.
Include ceiling square footage.
Paint Needed (Gallons) 1.9 gal (2 to buy)
Paint Needed (Liters) 7.19 L
Total Wall Area 333 sq ft
Total Coverage with Coats 666 sq ft
Editorial Standard

GetCalcu Methodology & Editorial Standards

Reviewed: September 2026

ASTM International standard specifications for construction materials and standard architectural coverage ratios.

Reference Sources: GetCalcu Construction & Building Estimations Board

How to Estimate Paint Coverage for Rooms

A gallon of quality interior paint covers approximately 350 to 400 square feet per coat.

Accounting for Openings

Standard doors subtract approximately 21 sq ft, while average windows subtract about 15 sq ft.

How to Use the Paint Calculator

  1. 1
    Enter room length, width, and ceiling height.
  2. 2
    Add number of doors and windows.
  3. 3
    Choose 1 or 2 coats.
  4. 4
    View required paint in gallons and liters.

Paint Calculator Formula

Gallons = Net Area × Coats / 350

Real-World Worked Examples

These scenarios demonstrate how key input parameters alter your calculation outcome.

12x12 Bedroom (8ft ceiling, 2 coats)

Input: 12x12x8, 1 door, 2 windows, 2 coats
Result: 1.91 Gallons (Buy 2 Gallons)

Frequently Asked Questions

How many square feet does one gallon of paint cover?

One gallon of paint typically covers 350 to 400 square feet on smooth, primed walls.