This calculator requires the use of Javascript enabled and capable browsers. Though it does intensive math calculations, it is a close estimator and enables the user to approximate the amount of paint required for a given room, based on parameters entered. It calculates the square footage of surfaces requiring paint, less that area occupied by doors or windows. It assumes the average door is 21 square feet in surface and the average window is 16 square feet. It takes into consideration spraying, which takes slightly more paint, or as the alternative, brushing or rolling, either of which requires roughly the same quantity of paint. It considers one or two applications. It also considers ceiling texture; standard texture is that of a similar appearance to the walls. Popcorn type ceilings and acoustical ceilings take up to 85% more paint for the same square footage as standard texture. Because of the varied heights and depths of such surfaces, we consider it as more square footage since in reality, it is just that. If you wish to paint the ceiling check one box or the other; you may also check both boxes if you feel the ceiling is very dry. Checking both will calculate a much higher square footage than actual but calculates very closely to the required quantity of paint. Enter the cost of the paint per gallon and the total price of the paint required is calculated. To do another, click the Clear Values button and then enter a new set of values. You may also wish to just change certain fields and recalculate. Calculated accuracy of current Javascript enabled browsers is generally 16 places. This does NOT take into consideration trim surfaces as being separate. If you are base coating, do a separate calculation and add the two together.