What is paint spread rate?

Spread rate (also called coverage rate) is the area one gallon of paint covers in one coat. Most interior latex paints cover 350–400 sq ft per gallon on smooth surfaces. Rough or porous surfaces may reduce coverage to 250–300 sq ft per gallon. Check the label on your paint can for the manufacturer's stated coverage.

How many coats do I need?

Two coats are standard for most interior painting projects — one to build an even base and a second for full, uniform coverage. Drastic color changes (e.g., dark to light) may require a third coat. High-quality paints sometimes achieve full coverage in one coat.

Why add a waste allowance?

Paint is lost to drips, roller nap absorption, and touch-ups after the job is done. A 10% allowance is typical for smooth walls. Add more (15–20%) for rough or textured surfaces, or if you expect significant touch-up work later.

Should I calculate ceiling and walls separately?

Yes, if your ceiling and wall paint differ (which is common). Run the calculator twice — once for wall area and once for ceiling area — or combine them if you are using the same paint throughout.

How do I account for doors and windows?

In Room mode, enter the number of standard doors (each ~20 sq ft) and windows (each ~15 sq ft) and the calculator subtracts their area from the paintable wall surface automatically.

Can I use metric measurements?

Yes. Toggle to Metric mode, enter dimensions in meters, and the results are shown in liters. The spread rate switches to square meters per liter automatically.

Paint Calculator

Name: Paint Calculator
Availability: InStock
Author: Nham Vu

Estimate how many gallons or liters of paint are needed for a room or any surface area, with a configurable number of coats and waste allowance.

Surface to Paint

Room Width (ft)

Room Length (ft)

Ceiling Height (ft)

Standard Doors

~20 sq ft each

Standard Windows

~15 sq ft each

Number of Coats

Paint Spread Rate (sq ft / gal)

Check your paint can label. Typical: 350–400 sq ft/gal.

Waste & Touch-up Allowance (%)

Results

Enter dimensions and press Calculate

Summary

Estimate how many gallons or liters of paint are needed for a room or any surface area, with a configurable number of coats and waste allowance.

How it works

Choose whether to enter room dimensions (width, length, ceiling height) or a custom surface area.
If using room mode, enter the room dimensions and optionally subtract doors and windows.
Select the number of coats you plan to apply (usually 2 for good coverage).
Enter the paint spread rate from your paint can label (typical: 350–400 sq ft per gallon).
Set a waste and touch-up allowance percentage (10% is recommended).
Click Calculate to see total paint needed in gallons and liters.

Use cases

Estimating paint for a bedroom, living room, or kitchen repaint.
Calculating primer and topcoat quantities before a renovation project.
Budgeting material costs for a whole-house interior painting job.
Determining how many paint cans to buy for a ceiling or feature wall.
Planning exterior painting projects by entering total wall area.
Comparing one-coat vs two-coat scenarios to decide on paint quality.

Frequently Asked Questions

Last updated: 2026-06-13 · Reviewed by Nham Vu