The math behind "mil"
A radian is the angle you get when you wrap an arc equal to the radius of a circle. A full circle is 2π radians (~6.283). A milliradian is one-thousandth of that — a very small angle.
At any distance, the linear size of 1 milliradian equals 1/1000 of that distance. That's the magic. At 100 m, 1 mil = 0.1 m (10 cm). At 1,000 m, 1 mil = 1 m. Distance and subtension scale linearly.
What 1 mil looks like at distance
| Distance | 1 mil (in) | 1 mil (cm) |
|---|---|---|
| 100 yds | 3.6" | 9.1 cm |
| 200 yds | 7.2" | 18.3 cm |
| 500 yds | 18.0" | 45.7 cm |
| 1,000 yds | 36.0" | 91.4 cm |
| 100 m | 3.9" | 10.0 cm |
| 1,000 m | 39.4" | 100.0 cm |
Range estimation — the mil-relation formula
If you know the size of the target and can measure how many mils it covers in your reticle, you can calculate distance:
Distance (m) = (target size in meters × 1000) ÷ size in mils
Distance (yd) = (target size in inches × 27.78) ÷ size in mils
Worked examples:
- A 1.8 m tall person fits in 3 mils → 1.8 × 1000 ÷ 3 = 600 m
- A 36" IPSC silhouette fits in 1.2 mils → 36 × 27.78 ÷ 1.2 = 833 yards
- A 12" steel plate fits in 0.5 mils → 12 × 27.78 ÷ 0.5 = 667 yards
Why mil clicks are usually 0.1
Most precision rifle scopes adjust in 0.1 mil increments. That gives you about 3.6 mm of precision at 100 m — finer than a shooter holding off a bipod could possibly use. Some hunting scopes go 0.2 mil or 0.05 mil; most factory tactical scopes settle on 0.1.
Mil vs MOA — quick reference
See MIL vs MOA for the full comparison. Short version: MOA is the inch-and-yards unit, MIL is the metric unit. Most modern precision optics ship in MIL. The math in your head is cleaner.
Mistakes that bite people
- Treating mil as a metric-only thing. It works equally well with inches/yards. 3.6" per 100 yards is the magic number.
- Mil reticle with MOA turrets (or vice versa). If you have a mil reticle, get mil turrets. Mismatch means you can't directly translate what you see into what you dial.
- Forgetting target size matters. The mil-relation formula needs an honest measurement of target size — a 17" deer chest pretending to be 18" will skew range estimation by ~6%.