It is very important to purchase a steering wheel cover that fits properly. The cover should not be loose. It should be tight against the wheel with a snug fit so it doesn't slip off the steering wheel when driving.
For some vehicles it will be necessary to measure your steering wheel to determine its size.
Two measurements are needed with instructions below.
Supplies:
Tape measure, painters tape (the blue kind), masking or scotch tape, pen and paper.