The window should be at least 20 inches wide and 32 inches high to give you enough clearance to exit safely. The windowsill width should be between a minimum of 6 inches and a maximum of 10 inches. Also make sure you measure the windowsill from outside to inside. Do not use the ladder on windowsills that are too large or too small for the hooks, damaged or weak, or blocked by furniture or security devices (grilles or bars). From the outside of your home, check below the window for any obstructions – trees, plants, bushes, windows, house fixtures, or any other objects in the direct path below the chosen window.