If you're interested in an exchange and are unsure of which style you want to try, measure your favorite pair of eyewear to get an idea of which Felix Gray frame would be the perfect fit! For reference, all frame dimensions are listed below.
A quick note on the Kepler frame - because of the different price points, if you wish to exchange from an all-acetate style to that one, you need to make a new purchase for the Kepler frame and return the current pair for a full refund! However, all other frames (that are priced at $95) are eligible for one-for-one exchanges.
| Frame (size) | Lens width | Nose bridge | Arm length | Lens height | Total frame width |
| Turing (small) | 45 mm | 21 mm | 140 mm | 37 mm | 126 mm |
| Roebling (small/medium) | 49 mm | 18 mm | 140 mm | 39 mm | 133 mm |
| Nash (medium) | 49 mm | 17 mm | 140 mm | 36.5 mm | 135 mm |
| Hopper (medium) | 49 mm | 18 mm | 145 mm | 38 mm | 135.5 mm |
| Kepler (medium) | 49 mm | 21 mm | 145 mm | 40 mm | 136 mm |
| Faraday (medium/large) | 53 mm | 17 mm | 145 mm | 36 mm | 136.5 mm |
| Jemison (large) | 52 mm | 18 mm | 145 mm | 41 mm | 140 mm |