Reticles
How to Read a Mil Dot Reticle
Quick answer
One mil equals exactly 3.6 inches at 100 yards by definition, so ranging a target is yards = inches x 27.78 / mils. Reading error is brutal on small subtensions: an 18 inch target read at 1.5 mil is 333 yards but at 1.4 mil is 357 yards, a 24 yard swing from one tenth of a mil on a scope like the Athlon Argos BTR GEN3 6-24x50 Riflescope, APRS11 FFP IR MIL Reticle.
A mil dot or mil-based reticle turns the space between its marks into a ruler, and the ruler is exact: one mil, short for milliradian, subtends exactly 3.6 inches at 100 yards by definition, scaling linearly with distance from there. That single fact is the whole basis for ranging a target by its size in the reticle rather than with a laser.
The math is only as good as two things you control: reading the reticle precisely, and, on a second focal plane scope, being at the one magnification the reticle was calibrated at. Get either one wrong by a small amount and the computed range moves by tens of yards, which is the part of mil ranging that trips up shooters who learned the formula but skipped the caveats.
How to range a target with a mil dot reticle
- Confirm your reticle actually reads in mils, not MOA. Check the reticle name in the product description before doing any math. Mixing mil subtensions with MOA arithmetic produces a wrong answer that looks plausible.
- If your scope is second focal plane, set the magnification to the calibrated power first. On a second focal plane scope, the reticle stays a fixed size in your eye while the image behind it grows and shrinks with magnification. Its mil subtensions are only correct at the single magnification the manufacturer calibrated them for, commonly the top of the range. Dial there before reading anything.
- Estimate the target size in inches as precisely as you can. The ranging formula is only as accurate as this input. A rough guess at target size produces a rough range no matter how precisely you read the reticle afterward.
- Read the number of mils the target spans, to the finest gradation you can resolve. Read tenths of a mil where the reticle allows it rather than rounding to the nearest half mil. The table below shows exactly what that rounding costs.
- Apply the formula: yards = target size in inches x 27.78 / mils read. This is exact arithmetic once the two inputs, target size and mils read, are accurate. An 18 inch target read at 1.5 mil computes to 333 yards.
- Cross-check with a laser rangefinder whenever one is available. Mil ranging is a genuinely useful skill and a real fallback, but a laser rangefinder such as the Vortex Diamondback HD 2000 Laser Rangefinder removes both sources of reading error at once. Use mil ranging as the backup, not the first choice, when a rangefinder is on hand.
- Verify a mil-ranged distance on a supervised range before relying on it for a shot at unknown range. Practice the whole sequence, estimate, read, compute, against known distances before trusting it under field conditions where the true range is not already known.
How much does a tenth of a mil of reading error actually cost you?
The relationship is exact division, which means a small reading error produces a disproportionately large range error as the subtension gets smaller, exactly where careless reading is most tempting.
A reading error of just one tenth of a mil swings the computed range by roughly 20 to 30 yards on an 18 inch target, which is why mil ranging rewards reading the finest graduation available rather than rounding to the nearest half mil.
Sourced figure
| Mils read | Computed range (18 inch target) |
|---|---|
| 1.2 mil | 417 yards |
| 1.3 mil | 385 yards |
| 1.4 mil | 357 yards |
| 1.5 mil | 333 yards |
| 1.6 mil | 313 yards |
| 1.7 mil | 294 yards |
| 1.8 mil | 278 yards |
Formula: yards = target size in inches x 27.78 / mils read. Second focal plane scopes must be at their calibrated magnification, usually maximum, for these subtensions to be correct at all.
One mil in inches, at distance
One mil subtends exactly 3.6 inches at 100 yards by definition and scales linearly, reaching 18.0 inches at 500 yards.
Sourced figure
| Distance | 1 mil subtends |
|---|---|
| 100 yards | 3.6 in |
| 200 yards | 7.2 in |
| 300 yards | 10.8 in |
| 400 yards | 14.4 in |
| 500 yards | 18.0 in |
Why second focal plane subtensions lie at every power except one
A second focal plane reticle sits behind the magnifying lens system and keeps a constant apparent size in your eye regardless of power, while the image of the target grows and shrinks as you turn the ring. That means the ratio between the target's image and the reticle's marks, the whole basis of ranging by mils, only holds true at the single magnification the manufacturer calibrated the reticle for.
A first focal plane reticle avoids this entirely by scaling with the image, so its subtensions read correctly at any magnification in the range. A scope such as the Athlon Argos BTR GEN3 6-24x50 Riflescope, APRS11 FFP IR MIL Reticle or the Arken Optics SH4 GEN2 4-16x50 FFP Riflescope, Illuminated VPR MIL Reticle, both first focal plane with a mil reticle, lets you range at 8x just as correctly as at full power. That flexibility is the main reason a first focal plane build is worth the added cost for anyone who ranges across a variable magnification range rather than always dialing to one fixed power first.
Sources
- Exact definition: 1 mil = 3.6 inches at 100 yards, scaling linearly with distance
- Owner-review consensus on first focal plane against second focal plane subtension accuracy
Frequently asked questions
What is 1 mil in inches at 100 yards?
Exactly 3.6 inches, by definition of the milliradian, and this scales linearly with distance: 7.2 inches at 200 yards, 10.8 inches at 300 yards, and so on. This figure never changes with cartridge, load or scope brand, since it is a property of the angular measurement itself, not of any specific product.
How do I range a target using mils?
Use yards = target size in inches x 27.78 / mils read in the reticle. Estimate the target's real size as precisely as possible, read the number of mils it spans using the finest gradation your reticle allows, then apply the formula. An 18 inch target spanning 1.5 mil computes to 333 yards.
Why does my mil-ranged distance not match my laser rangefinder?
The two most common causes are reading error, since a tenth of a mil of misread subtension swings the answer by tens of yards on a small target, and being at the wrong magnification on a second focal plane scope, whose mil subtensions are only correct at one calibrated power. Confirm both before assuming the target size estimate was wrong.
Does mil ranging work the same at every magnification?
Only on a first focal plane scope, where the reticle scales with the image and its subtensions stay correct across the whole magnification range. On a second focal plane scope, the mil marks are only accurate at the single magnification, typically maximum, that the manufacturer calibrated them for.
How much does a small reading error actually matter?
On an 18 inch target, reading 1.5 mil instead of the true 1.4 mil shifts the computed range from 357 yards to 333 yards, a 24 yard swing from a tenth of a mil of misread subtension. The smaller the mil reading, meaning the farther or smaller the target, the larger the resulting range error from the same reading mistake.
Can I use a mil reticle with MOA turrets?
You can mechanically, but it invites confusion, since holding over in mils and dialing in MOA requires converting between two different, non-interchangeable units every time. Most shooters are better served buying a scope where the reticle unit and the turret unit match from the factory.
Researched, not professional advice. This page is compiled from published manufacturer specifications, published optical and ballistic formulas, and owner-review consensus, not hands-on testing. Figures described as a rule of thumb are shooter convention rather than sourced numbers, and they are labelled that way wherever they appear. Ballistic figures come from a point mass model using the ballistic coefficient the maker publishes, so treat them as a starting point and confirm them on paper at a measured distance. Confirm your firearm is unloaded with the action open before you mount, level, torque or bore sight anything. Verify a zero only on a supervised range or a safe, legal backstop, know what lies beyond your target, and follow the law where you hunt and shoot, including rules on land access and permitted cartridges.