For traditional chairs (The back and seat are two separate pieces. Typically, they two pieces are attached at a 90 degree angle.)
HOW TO MEASURE YOUR CHAIR. You need:
(A) the height of the chair back from the seat to the top of the chair
(B) the width of the chair back at the widest point
(C) the depth or thickness of the chair back at the thickest point of the chair back
Send me these measurements. A picture of your chair is also helpful to determine if additional reinforcement is needed for your chair.