Step 2: Measure the inside of the frame in the back of the sofa, this one measures 69" wide.
Step 3: Take the the front and back measurements which are 69", you would order 69" wide seat cushions (3 each 23" wide).
Step 4: Take the measurement of the depth of the sofa, from the front rail to the back, add 1". This on measures 23" deep, so you would order 24" deep cushions.
Step 5: Measure from the floor to the top of the seat deck. The ideal seating height is 18-19". This one measures 12 1/2" high, therefore we would order 6" thick cushions to make the top of the cushion 18 1/2" off the ground.
You would order a 69" wide in front x 69" wide in back x 24" deep, x 6" thick seat cushions (3 cushions that are 23" wide x 24" deep x 6" thick).
Step 6: Measure the width of the sofa back. This one measures 69" wide, so you would order 69" wide back cushions (3 each 23" wide). Usually the seat and back cushions are the same width.
Step 7: Measure the height of the back from the top of the deck to the top of the sofa, then take off the seat thickness. This one measures 25" high. Deduct the thickness of your seat cushion from the total height to determine the back height. You would order a 19" high back cushion. It's also good to measure the back of your old cushions. It's OK if the back cushions extends over the the frame. The average size is 19" - 20" high anything lower than 18" is uncomfortable.
Step 8: Back cushions are usually 4 or 6" thick. If your seat depth is 22" or under order a 4" thick back cushions with buttons. If your seat depth is 23" or over order a 6" thick back cushions without buttons.
Step 9: Does your sofa back curve on the top or go straight across? You have the option of either style. This one has a curved top, so you would order a curved top (each back end cushion would have 1 curved top and the sofa center would go straight across).
You would order a 69" wide x 19" high x 6" thick back cushions with a curved top (3 cushions that are 23" wide x 19"high x 6" thick).
Remember to measure twice and call if you have any questions!