![](https://cdn.shopify.com/s/files/1/2574/2560/files/Bicep_1.png?v=1664490707)
Step 1: Lay the completely buttoned jacket flat on a table facing up with the collar up, and the arms positioned to the side. Use your hands to gently extend and flatten out excess fabric.
![](https://cdn.shopify.com/s/files/1/2574/2560/files/Bicep_2.png?v=1664490774)
Step 2: Beginning at the edge of the armhole seam (at the armpit point) measure horizontality the distance between this point and the edge of the sleeve.