Scope Mount Finder

AR-15 red dot and LPVO mount height

The standard AR-15 optic heights, what each one lines up with the iron sights, and when to run the taller 1.93 inch mount.

Rail cross-section, not to scale
Designationcowitness and 1.93
Rail standard
Absolute cowitness
about 1.42 in optical centre
Lower 1/3 cowitness
about 1.5 to 1.57 in
Heads-up height
1.93 in for red dots and LPVOs
Standard LPVO cantilever
about 1.5 to 1.54 in

On an AR-15 the mount height sets where the dot sits against the iron sights. Absolute cowitness puts the dot at about 1.42 in so the irons sit in the middle of the window. Lower 1/3 cowitness at about 1.5 to 1.57 in puts the irons in the lower third.

The 1.93 in height lifts the optic for a heads-up posture, which many shooters prefer for red dots and for LPVOs, where the tighter eye box makes a repeatable head position matter more.

Most one-piece LPVO cantilever mounts ship around 1.5 to 1.54 in, giving an absolute-style cowitness. Pick the height by the posture you want and by whether you need to cowitness irons.

AR mounts by height
Related

Sources: Best height for a red dot, Primary Arms · AR-15 red dot cowitness guide, Swampfox · LPVO mounting height guide, Swat Optics