Measure the width from arm to arm, as this is the largest part of your sofa. For the height, you want to measure the back at the highest point. Measure with the sofa legs already attached, as that will give you the right idea of what you can expect here. Also, measure the depth of the sofa, since this is also very important. Diagonal depth can be measured by placing your tape measure from the top back of the frame to the bottom front.