Is there a way to measure fork offset while the fork is on the bike?
I have what appears to be a replacement track fork on a road bike.
I would like to get a road fork with about 45mm of offset, but wish to know the offset on existing (installed) fork before making a new purchase.

TIA

You could try: Put bike in workstand. Tie front wheel to DT to stop it moving around (it doesn't matter if it's not lined up with the DT). Get head-tube vertical (compared to a plumb-line). Mark where plumb-line touches floor. Then move the plumb-line to the axle and mark where that touches the floor. The distance between the two marks should be the offset. If it's about 45mm then it's probably exactly 45mm since most road forks are 45mm.

Good idea. Thanks.