Every sofa is different but we've managed to classify them down to several standard shapes and sizes.
To get a broad understanding, check this article out: How To Measure Sofa
If you've placed an order that requires measurements done, you would have received an e-mail leading you to the Measure Tool which would guide you throughout the process.
For more specific instructions, it will have to depend on your sofa's structure in which case please get in touch with us via e-mail.