Two to three gallons of paint typically suffice to cover 700 square feet. One gallon of paint covers up to 400 square feet, depending on the brand of paint, the surface of the wall and whether the color change is dramatic or subtle.
To calculate the number of gallons necessary, check with the manufacturer to determine the average amount of space that particular product covers. Keep in mind that previously unpainted, porous or rough surfaces typically require more paint than smooth, sealed surfaces ones. Likewise, more paint is generally needed when making a drastic color change, which usually requires multiple coats. Subtle colors changes may only require a single coat of paint.