Paint Calculator — How Much Paint Do I Need?

Your Paint Project Guide

Painting a room is one of the most popular DIY home improvement projects, and for good reason — a fresh coat of paint transforms a space for a fraction of the cost of other renovations. But buying the wrong amount of paint means either extra trips to the store mid-project or leftover gallons collecting dust in your garage. This paint calculator takes your room dimensions, accounts for doors and windows, and tells you exactly how many gallons you need.

Most interior latex paints cover 350 to 400 square feet per gallon on smooth drywall. If your walls have a textured finish, heavy stucco, or unpainted drywall, plan on closer to 300 square feet per gallon because the surface absorbs more paint. Always check the coverage listed on your specific paint can, since premium paints sometimes offer better coverage per gallon.

Two coats is the standard recommendation for most paint jobs. Even if the new color looks great after one coat, a second coat ensures uniform coverage, better color depth, and improved durability. If you're making a dramatic color change — say, going from dark red to light gray — you may need a coat of primer plus two coats of finish paint, or three coats of a paint-and-primer combination.

Prep work makes or breaks a paint job. Spend time filling nail holes with spackle, sanding rough spots, and taping off trim and ceilings before you open the first can. A good painter's tape like ScotchBlue gives you crisp lines without pulling off existing paint when you remove it. For the smoothest finish on walls, use a 3/8-inch nap roller cover — thicker naps are for textured surfaces.

Here's a tip from professional painters: always buy your paint in one batch. If you run out and buy more later, even the same color code can have slight variations between batches. Buying one extra quart for touch-ups down the road is much smarter than trying to color-match later. Store leftover paint in a cool, dry place with the lid sealed tightly — it stays usable for years.

This calculator focuses on wall area only. If you're also painting the ceiling, measure it separately (length times width) and add that to your total. Ceiling paint is typically a flat finish in white, and a gallon covers roughly the same 350 to 400 square feet.