That depends on what manufacturer you are measuring for. If you look at our Sizing Charts page, you can find sizing forms that have diagrams for needed measures. Using a soft tape measure (do not use a carpenter's tape measure; it needs to conform cleanly to the body), follow the diagrams using a partner to assist you for accuracy. If you have any questions to make sure you are doing it right, feel free to give us a call. We always are happy to help you with any questions you may have.