How do you know how many meters away you are in Battlefield 3 when sniping?

I noticed that when people talk about Battlefield 3 sniper shots, they often include the distance of the shot in meters. How do you calculate this distance in game?How do you know how many meters away you are in Battlefield 3 when sniping?
after a long distance headshot, it'll sayHow do you know how many meters away you are in Battlefield 3 when sniping?
Until you take the shot, its down to judgment of distance. How I work it out is, when taking the shot, the amount you have to aim ahead (because you have to allow time for the bullet to travel) Is roughly around a certain distance.



100m or less and you shouldn't have to predict movement

200m around 1 second ahead

300m around 3 seconds ahead

and anything higher you will notice because when scoped in (without zooming) it should be a unclear/distorted image.How do you know how many meters away you are in Battlefield 3 when sniping?
If you get a marksman headshot or marksman kill it tells you, otherwise at the end of the game it tells you what your farthest kill shot was by meters