Painting & wallcovering calculators

Estimating paint and wallpaper

The paint calculator estimates gallons of paint and primer for walls, ceilings and trim from the room size, the number of coats and the surface texture, after deducting doors and windows. The wallpaper calculator counts rolls by whole drops, allowing for pattern repeat, so you do not come up one strip short at the last wall.

Most interior latex paints cover roughly 350 to 400 square feet per gallon per coat on smooth, primed drywall; the label on the can gives the exact figure. Textured, porous and bare surfaces take more, and a strong color change usually needs a primer plus two finish coats. Buying a little extra from the same batch saves color-matching a touch-up later. For wallpaper, allow at least one extra roll, more for a large pattern repeat.

Exterior siding paint uses the same coverage math; the siding calculator in the roofing and siding section gives the wall area to start from. If you are hanging new drywall first, the drywall calculators cover sheets, mud and tape.

Homes built before 1978 may contain lead paint, and contractors disturbing it must follow the EPA Renovation, Repair and Painting rule. That, exterior work above one story and spraying in occupied buildings are the usual reasons to bring in a professional painter.

How each calculator is specified, tested and corrected is described on our methodology page.