Binoculars Range Calculator (distance from a mil-reticle reading and a known size)

Understanding the binocular rangefinder (mil) calculator — concept and principle

Many binoculars and scopes have a reticle marked in mils. If you know the size of an object, its apparent size in mils tells you how far away it is. This calculator applies the mil relation and the exact trigonometric form, with a choice of milliradian or NATO mils.

One milliradian is 1 m at 1,000 m, so 1.8 m filling 5 mils is 1.8 × 1000 ÷ 5 = 360 m away.

How it is calculated

Milliradian reticle: distance = size × 1,000 ÷ mils.
NATO mils divide a circle into 6,400 parts; 1 NATO mil ≈ 0.982 mrad, so the distance is slightly larger for the same reading.
Exact form: d = size ÷ (2 tan(θ ÷ 2)), with θ in radians.
Angle in degrees = θ × 180 ÷ π; yards = metres ÷ 0.9144.

The principle

For small angles, arc length s = rθ. One milliradian is the angle that covers 1 m at 1,000 m, so an object covering 5 mils is at a distance of 1,000 ÷ 5 = 200 times its size. The small-angle form and the exact form differ by a negligible amount at reticle angles. Accuracy depends mostly on how well you know the object's size and how precisely you read the scale.

Worked example

Default inputs: object 1.8 m tall, reading 5 mils, milliradian reticle.

Distance = 1.8 × 1,000 ÷ 5 = 360 m; the small-angle estimate is also 360 m.
In yards = 360 ÷ 0.9144 ≈ 394 yd; in km = 0.36 km.
Angle subtended = 0.005 rad × 180 ÷ π ≈ 0.286°.

Each point is the calculator re-run with only “Reticle reading (mils)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Reticle reading (mils)	Distance to the target (m)
1.25	1,440
2.5	720
3.75	480
5	360
6.25	288
7.5	240
10	180

How to read the result

Range estimates are sensitive to reading errors: half a mil at 5 mils is already a 10% change in distance. Use the largest known dimension you can see clearly, and take several readings. For animals or vehicles, sizes vary, so treat the result as an approximation.

Common mistakes

Using a NATO-mil reticle with the milliradian formula, or vice versa.
Guessing the object's size poorly.
Measuring part of the object (for example, only the visible portion behind cover).
Using MOA reticles with mil formulas.

Keep in mind: Mil ranging gives approximations. Do not rely on it where safety depends on an exact distance; follow local laws and safety rules.

Frequently asked questions

How do I calculate distance with a mil reticle?

Distance = object size × 1,000 ÷ mils, using the same unit for size and distance.

What is the difference between a milliradian and a NATO mil?

A milliradian is 1/1,000 rad (about 6,283 per circle); a NATO mil is 1/6,400 of a circle.

How accurate is mil ranging?

It depends on the size estimate and reading precision; errors of several per cent are common.

Sources: US Army Field Manual FM 3-25.26, Map Reading and Land Navigation (mils) · NIST Special Publication 811 (radian and angle units)

Checked 9 Nov 2026. Arc length s = rθ (OpenStax, University Physics Volume 3 (2016), §4.5); definitions of the milliradian (10⁻³ rad) and the NATO mil (2π/6400 rad) and of the yard (0.9144 m) — standard values.

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