How is the field goal distance calculated in American football?

Question

I wonder how the position is calculated in American football:

1. The position that the snapper snaps
2. The position in that the holder fixes the ball and the kicker kicks.

For example, in the record breaking 66-yard field goal of Justin Tucker on Week 3 of 2021 season between the Baltimore Ravens and Detroit Lions,

The previous play was stopped at DET 48. When I see the video, the snapper snapped at DET 50 instead of DET 48. Why did they withdrew two yards, and why is the kick 'just' six yards behind the snap, not five or seven lines?

Last play before the kick The snap The kick

Play-by-play record: https://www.espn.com/nfl/playbyplay/_/gameId/401326366 Video:

Answer 1

The previous play was stopped at DET 48. When I see the video, the snapper snapped at DET 50 instead of DET 48.

Not that I can see. The angle is different, so it's difficult to tell. But you can see that the player on the left end of the line (on the right side of the frame) has his foot on the 50. The ends of the line will be well back from the snap position, so it looks to me like the ball is made ready somewhere near the 48, but definitely closer than the 50.

In the low-angle replay, it's hard to see the actual distance, but the ball is well beyond the hash mark on the 50. And the yard line marking the 49 to the rear is closer than the ball. So 2 yards forward of the 50 seems plausible.

That would make the kick from the Baltimore 44 to be 8 yards behind the line of scrimmage, which is common.

There's an answered question about why the distance is 8 yards.