How many mm would my chin need to be moved so that it is even with my lower lip? (Photo)

I perform genioplasties of all types (sliding, complex sliding, augmentation, reduction, grafting, combinations, etc) and each case deserves a different amount of mm in, for example, advancing the chin.

It's better you focus in designing the chin you deem ideal and then discuss it with your surgeon for any optimizations, then your surgeon will plan accordingly the mm.

Your chin is really small, has microgenia and it is not a receded one, you might fit better into a bone-grafted augmentation genioplasty.

Dear Affectionate,

Thank you for sharing your profile photo. Since you don’t have any bite or occlusion issues, you would be a reasonable candidate for a sliding genioplasty (chin advancement).
From your photo, it looks like your chin is somewhat recessed relative to your lower lip. Exact millimeter movement (often in the range of 4–8 mm forward) can only be determined with proper facial analysis, cephalometric X-rays, and surgical planning software. These tools allow precise measurement so that your chin is advanced to a point that is balanced—not too far forward, and not leaving you under-projected.
The good news is that genioplasty is very customizable. Your surgeon can advance, vertically adjust, or contour the chin bone in a way that harmonizes with your facial features, while also avoiding an unnatural or “witch chin” appearance.
An in-person consultation with a board-certified oral & maxillofacial surgeon or plastic surgeon will give you an accurate measurement and a surgical plan that best suits your facial proportions.

Warmly,

Earl Stephenson, Jr, MD, DDS, MBA
ESJ Aesthetics — “Where Confidence Takes Shape!”

The profile photo shows significant horizontal imbalance, so I would likely move the chin forward 8-9 mm with a sliding genioplasty. This will improve your facial balance. The limit of moving the chin forward is 10 mm.