The Paint for a Room calculator estimates the number of gallons of paint needed to cover a rectangular room based on the length, width and height of the room.
INSTRUCTIONS: Choose units and enter the following: 
- (L) Length of Room
- (W) Width of Room
- (H) Height of Ceiling
- (CT) Number of Coats
- (WD) Number of Windows
- (DR) Number of Doors
Gallons of Paint for a Room (GP): The calculator computes the amount of paint needed for the entire room in gallons, and the total surface area including the ceiling in square feet. The calculator also returns the same for just the wall (no ceiling). However, these can be automatically converted to compatible units via the pull-down menu.
The Math / Science
The calculator computes the surface area of the room including the ceiling and for the walls only. It then divides those areas by the paint coverage area (PC = 400 ft²/gal) to compute the number of gallons of paint. Most manufacturers call for one gallon of paint to cover between 400 and 450 square feet (ft2) of wall or ceiling. The formula for the surface area of a room is:
`A = 2*L*H + 2*W*H + W*L`
`A = A - (WD*15ft^2 + DR*21ft^2)`
where:
- A = Surface Area of the room including the ceiling
- L = Length of Room
- W = Width of Room
- H = Height of Ceiling
- WD = Number of Windows
- DR = Number of Doors
Paint is used for walls in rooms around the world. In addition to aesthetics, paint provides protection for the wall materials and extends their life. Paint also provides sanitary benefits. Many governments require the painting of apartments (flats) for each new tenant.
Often ceilings are painted with different paint since they tend to have less contact with people and other things, and because ceilings make for nice accent (lighter) surfaces.
Room Calculators
- Volume of a Room: Computes the cubic feet (volume) of a room based on its height, length and width.
- Areas of a Room: Computes the total square feet (area) of a room based on its height, length and width. This includes the total area of the ceiling and walls for things like paint. It also individually includes the area of the ceiling, walls and floor of a room.
- Room Paint Cost: Estimates the gallons of paint needed and associated cost to paint a room based on the room dimensions, number of coats and the unit cost of paint per gallon.
- Wallpaper for a Room: Computes the number of rolls of wallpaper needed to cover the walls of a room based on the dimensions of the room and the rolls of wallpaper.
- BTUs per Hour to Heat a Room: Computes the energy (heat) required to heat a space of a certain volume by a specified temperature variance.
- Insulation Rolls for Walls of a Room:
Computes the number of rolls or batts of insulation needed for the WALLS of a room based on the length and height of the four walls. The calculator assumes standard 16" spacing on the studs. - Drywall Materials for a Room: Computes the number of drywall boards (4x8 or 4x12), number of drywall nails or screws and gallons of joint compound need for a room based on the room's dimensions.
- Ceiling Tiles for a Room: Computes the number of ceiling tiles needed to cover the ceiling of a room based on the dimensions of the room and the tiles.
- Cost of Flooring a Room: Computes the square feet of a room and then applies the price per square feet of different flooring products (e.g., hardwood, carpeting, tile)
- Room Framing Cost: Computes the number of studs and plate boards for a room and estimates the cost of framing based on the unit price of the lumber.
- Outlets and Wiring for Room: Computes the number of outlets (boxes) and length of wire to connect them in a room based on the room dimensions and the outlet spacing.
Paint Calculators:
- Paint for a Room: computes the number of gallons of paint or primer needed to paint an entire room, the four walls and ceiling and also for just the walls.
- Paint for a Wall: computes the number of gallons of paint or primer needed to paint a wall or any rectangular area (wall or ceiling).
- Exterior Paint for a House: computes the number of gallons of exterior paint for a gabled building like a common house.
- Cost to Paint or Primer a Room: (CLICK HERE)
- Cost to Paint a Wall: (CLICK HERE)
- Cost to paint or prime a ceiling: CLICK HERE
- Paint Pricing Survey
Paint Pricing Survey Data
One should use the pricing for paint or primer that can be bought locally since prices may vary. However, the following prices are recent U.S. dollar costs for one gallon of paint or primer in the United States:
- Paint Pricing Survey date: 7/29/22
- Paint Price Survey Source (online): HomeDepot
- Price of premium (high quality) paint: $61.94 USD
- Price of medium grade paint: $48.98 USD
- Price of economy paint: $26.98 USD
- Price of primer: $19.98 USD