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
- Number of gallons to paint or primer a room.
- Cost to paint or prime a room.
- Surface area of the interior walls of a room
- Surface area of the interior walls and ceiling of a room.
- Floor area of a room
- Volume of a room
- Energy (BTUs/hr) needed to heat a room
- Insulation for a Room
- Number of Studs in a Room
- Number of drywall sheets needed for a room
- Cost of studs needed to frame a room
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