The average size of a sofa is from 5' to 6' wide and 32" to 40" in height. A good rule of thumb is to allow one foot of space around your sofa to accommodate traffic and legroom. If you're looking for a sofa that will grant you a little more sitting space than average, you can opt for something longer from 87" to 100" or go extra-long one with a length of over 100". A standard sofa measures 25" deep, although most sofas have a depth ranging from 22" to 26".