Paint Calculator

How this paint calculator works

Use this room paint calculator for bedrooms, living rooms, offices, rentals, and other interior spaces. Enter length, width, wall height, door count, and window count. The calculator estimates wall area, subtracts standard door and window areas, multiplies the paintable area by coats, and rounds gallons up from the coverage per gallon assumption.

Default coverage is 350 square feet per gallon and default coats is two. Real coverage depends on surface texture, color change, primer, roller nap, paint quality, and application method.

Paint coverage reference table

Measuring notes

Measure wall height from finished floor to ceiling. Count standard doors and windows only when they are not painted as wall surface. For accent walls, estimate that wall separately by entering custom dimensions or reducing the room dimensions.

Coverage depends on the surface you are actually painting. Smooth primed drywall usually comes closest to the label coverage, while textured walls, patched areas, porous surfaces, and strong color changes can use more paint. If the current wall color is much darker than the new color, plan for primer or an additional coat. If the new color is deep or highly saturated, check the product guidance because some colors need a tinted primer or extra coats for even appearance.

Doors and windows reduce wall area, but they do not always reduce labor. Masking, cutting in, moving furniture, and working around trim can take time even when the paintable square footage is lower. For rooms with many openings, built-ins, or accent walls, use the calculator for paint quantity and then add time for preparation. If the ceiling, trim, closets, or doors will also be painted, estimate those items separately because they often use different products and sheens.

Before buying, confirm container sizes. A result that rounds to two gallons may be cheaper or easier to manage as a gallon plus quarts depending on the product line and expected touch-ups. Keep a small amount of labeled paint for repairs, especially in rentals, hallways, and children’s rooms.

Regional pricing notes

Paint pricing varies by brand, sheen, product line, colorant, and local promotions. Labor varies with patching, masking, ceiling height, occupied rooms, and whether trim or ceilings are included.

Regional conditions also affect planning. Humidity, ventilation, and temperature influence drying time. Older homes may require extra surface preparation, and homes built before lead-safe rules may need special care when disturbing painted surfaces. If you are painting a kitchen, bathroom, or laundry area, choose a product suited to moisture and cleaning. If you are painting a rental turnover, speed and durability may matter more than lowest material cost.

When to call a professional

Professional help is worth considering for tall stairwells, extensive patching, lead-safe renovation concerns, sprayed finishes, cabinet work, or spaces where masking and surface preparation are the majority of the job. A calculator can estimate gallons, but it cannot judge adhesion, substrate condition, or the finish quality required for a visible room.

Buying and ordering tips

Buy enough paint from the same product line, sheen, and color formula to finish the room without switching batches mid-wall. If the estimate is close to a container boundary, round toward having extra because touch-ups are easier when the same paint is available. Label leftover paint with room name, date, sheen, and color code. For rentals or high-traffic spaces, include patching supplies, tape, drop cloths, rollers, brushes, trays, and cleanup materials in the budget. Test patches are also useful when sheen, lighting, or wall texture could change how the final color appears. Save the can label for later matching.

FAQ

Does the calculator subtract doors and windows?

Yes. It multiplies door and window counts by editable subtraction assumptions.

How many coats should I use?

Two coats is a common planning default. Use more for major color changes or uneven surfaces.

Should primer count as a coat?

Primer is tracked as an assumption, but paint gallons are calculated from paint coats.

Why round gallons up?

Paint is bought in containers, and running short can create color and sheen differences.

Does this include ceilings?

No. This room calculator estimates walls. Estimate ceilings separately using their area and coverage.

Is trim included?

No. Trim, doors, cabinets, and specialty coatings should be estimated separately.

Sources and assumptions

Last updated 2026-05-04. The calculator uses the cited reference above, common retail package labels, and editable default assumptions for planning quantities. Confirm product coverage, package yield, price, and local requirements before purchasing materials or scheduling work.