Measure out the perimeter of the room i.e the entire length of the four sides of the room or as the case may be.
Then measure out the height of the room, the length from floor to the ceilling. These could be in meters or in feet depends on what you are used to.
Now calculate the surface area of the room which is simply by multiplying the total length of the room by the ceilling height.
For a standard Nigerian room, it is usually 3.6m x3.6m or 12ft x12ft others can also make theirs 3.6m x3.0m or 12ft x 10ft etc depending on the plan of the house.
After this measure out the openings in the room, most often the windows and doors.
For windows it may be 1.2m x 1.2m i.e 4ft x 4ft or 1.8m x 1.2m i.e 6ft x 4ft, the height of windows are mostly 1.2m or 4ft while the length is what usually varies. Multiply the height by the length of all the windows and then do same for doors.
For doors the height is usually 2.1m or 7ft and the length is 0.9m or 900mm or 3ft do multiply the height by the length and sum the total areas of openings in the room then subtact from the total surface area of the room earlier measured.
After determining your area (square feet or m2) then choose your paint check the label of the paint bucket for the spread rate for the paint. Spread rate is just the number of square feet (m2) of surface each coat of paint will cover.
After finding out, divide the total surface area you measured earlier by this number to determine the number of paint bucket/liter you will need for each coat.
The number of coats you should apply depends on the type of paint, the colour, the nature of the colour you are applying, method of application and the nature of the surface.
For example, you will likely need a second coat of paint when covering a dark color with a lighter one. Also, certain surfaces, like exterior masonry, are very porous and absorb a great deal of paint. In such cases, a second coat is often needed to give the paint a uniform appearance.
Using a brush will put on a heavier, better-hiding coat than roller application.
-culled from http://www.buildingcontractorsecrets.com
