Mirror Installation Instructions Warning: Always wear safety goggles and gloves when working with mirror ta avoid personal injury. How many to buy? Each Mirror tile is one sq.ft. in size in). 1. Measure the height and width of the area to be covered. 2. Multiply these two numbers. Total is the number of Mirror-Tiles you need. Example: 8 ft. high by 12 ft. wide by wall area. 8ft. You'll need 96 Mirror tiles. If there are windows or door spaces, deduct that spare footage from the total.