How to Choose Your Size: Just measure your window s width and round DOWN to the nearest 1/2" size. Pick a width slightly smaller than your window s exact measurement: If your window is 30 7/8" wide choose 30 1/2". If your window is 30 1/8" wide choose 30". No Drill Design: A solution to cover your windows without the hassle of drilling holes and install the shades without tools in 30 seconds. Easy as that! Cordless & Free-Stop System Smooth and quiet glide spring system provides a clean and tangle-free look and creates a safer environment for both children and pets. It will stay at whatever position you stop and can be easily raised or lowered with the touch of a finger.