About This Tool

### About the Paint Calculator Whether you are refreshing a single room or painting your entire home, knowing exactly how much paint to buy is essential for staying on budget and avoiding wasteful extra trips to the store. This free paint calculator takes the guesswork out of your painting project by calculating the precise amount of paint you need based on your room dimensions, number of coats, and coverage specifications. The calculator works by computing the total wall area for each room using the perimeter and ceiling height, then subtracting standard-sized openings for doors (21 square feet each) and windows (15 square feet each) to determine the actual paintable surface. It then applies your chosen waste factor -- typically 10% -- to account for roller absorption, uneven surfaces, and paint left in trays and brushes. You can add multiple rooms to a single calculation, making it easy to plan a whole-house painting project at once. The tool supports customizable paint coverage rates (most paints cover 350-400 square feet per gallon), number of coats (two coats are recommended for most projects), and your paint's cost per gallon. The result gives you the total gallons needed, overall paint cost, and cost per room so you can budget accurately before heading to the paint store.

Key Features

**Multi-Room Support**: Add as many rooms as you need and calculate total paint requirements for your entire project in one go, with per-room cost breakdowns.
**Automatic Opening Deductions**: Automatically subtracts standard door and window areas from your wall calculations so you only buy paint for surfaces you will actually cover.
**Adjustable Coat Coverage**: Choose between 1, 2, or 3 coats of paint and see how each option affects the total gallons needed and overall project cost.
**Waste Factor Included**: Applies a configurable waste percentage (default 10%) to account for paint lost during application, ensuring you have enough material to finish the job.
**Instant Cost Estimation**: Enter your paint price per gallon to get an immediate total cost estimate and average cost per room for easy budgeting.

Frequently Asked Questions

How many coats of paint do I need?

For most interior painting projects, two coats are recommended for the best coverage and most uniform finish. A single coat may be sufficient if you are repainting with the same color or using a high-quality paint-and-primer combination. Three coats may be necessary when painting over dark colors with a lighter shade, covering stains, or using certain paint finishes like flat or matte that tend to show lap marks with fewer coats.

How much area does one gallon of paint cover?

One gallon of paint typically covers 350-400 square feet of smooth surface with one coat. However, actual coverage depends on several factors including the texture of your walls (textured surfaces absorb more paint), the type and quality of paint, the application method (rollers generally use less paint than brushes), and the color change involved. Porous or unpainted surfaces like new drywall may require a primer first and will absorb more paint on the first coat.

How do I calculate paint for rooms with vaulted or cathedral ceilings?

For rooms with non-standard ceiling heights, use the average wall height in the calculator. Measure the height at the shortest and tallest points of each wall, then use the average. For example, if a wall with a vaulted ceiling goes from 8 feet to 14 feet, enter 11 feet as the height. You may also want to increase the waste factor slightly to account for the additional complexity and difficulty of painting higher areas.

Paint Calculator - Free Online Calculator

Rooms

Paint Details