Since every pair of custom frames is made specifically for the client, I will take various measurements in order to insure the proper sizing and fit of the spectacles. There are various methods of acquiring these measurements.
I can personally take measurements if we arrange an appointment at my workshop. I will observe how the current frames fit, suggest trying on a few pair of my spectacles and pull out the calipers to note a few concrete measurements.
Alternatively I am able to obtain measurements remotely. I will provide a few sample images to be mimicked with a pair of well fitting frames. Additional images wearing these frames will also help me to determine how those frames fit and ultimately determine the best fit possible for the specs to be made.
Also under consideration at this point are any thoughts about how spectacles have fit in the past, or improvements and alterations to a fit that may have been noticeably bothersome. Perhaps one ear is higher than the other. This is when we figure out these details.