A laser rangefinder is the fastest way to a distance, until the battery dies, the target will not return a clean reading, or you simply left it behind. Long before lasers, shooters ranged targets with the marks already in their scope, and that skill still works when the electronics quit. The marks on a mil reticle are a measuring stick, and with one known target size and a little arithmetic they become a backup rangefinder you can never leave at home. This is a guide to the mil relation formula, worked in plain steps, so your hash marks can put a number on a target when nothing else will.
Why learn this when you own a laser
It is fair to ask why bother, since a good rangefinder is fast and accurate. The answer is redundancy, because the laser is the one piece of your kit most likely to fail at the worst moment. Batteries die in the cold, a target against the sky or through brush will not bounce a clean return, and a dropped unit can simply break, leaving you with a target and no number.
Reticle ranging is the method that predates and backs up the laser, and it needs nothing but your scope and your head. It will not match a laser for speed or precision, but it turns a no-read situation into a usable estimate, which is what separates taking a shot from packing up. For a field shooter far from a spare battery, that backup is worth the small effort to learn.
There is a second benefit worth noting. Learning to range with the reticle teaches you to read the subtensions in your glass fluently, which sharpens every hold and correction you make with the reticle, laser or not. The skill pays off long before the battery dies.
The angle that makes it work
The method rests on one property of the milliradian, the mil. A mil is an angle equal to one one-thousandth of a radian, and the useful consequence is that one mil always subtends one one-thousandth of the distance, whatever that distance is. At 1,000 yards a mil covers one yard, at 500 yards it covers half a yard, and the proportion never changes.
That fixed proportion is the whole trick. Because a mil is a constant fraction of the range, the apparent size of a known object in your reticle tells you how far away it is. A target that covers two mils is half as far as the same target covering one mil, since it appears twice as large, and that relationship is exact rather than a guess.
So the reticle is a protractor laid over the target. Measure how many mils a known-size object spans, and you have measured an angle, which the constant proportion of the mil converts directly into a distance. Everything else is just plugging numbers into that relationship.
The mil relation formula
The formula comes in a metric form and an imperial form, and both say the same thing. In metric it is the cleanest: range in meters equals the target size in meters times one thousand, divided by the size in mils. A target one meter tall that spans two mils sits at 500 meters, because one times one thousand divided by two is five hundred. The metric version is why mil reticles and meters pair so naturally.
In yards and inches the formula carries a conversion constant: range in yards equals the target size in inches times 27.8, divided by the size in mils.1 The 27.8 comes from the geometry, since a mil is 3.6 inches at 100 yards, and it folds the unit conversion into one number you can memorize.2 The math is the same proportion, just expressed for the units most American shooters use.
Both forms need exactly two inputs, the true size of the target and the mils it spans in your reticle. Measure the mils carefully, supply a true size, divide, and you have a range. The arithmetic is simple enough to do in your head with round numbers and on paper when it counts.
A worked example
Make it concrete with a common reference. Say you are looking at a steel target you know is 24 inches tall, and it spans 1.5 mils in your reticle. Using the imperial formula, range equals 24 times 27.8 divided by 1.5, which is about 445 yards. That is a usable firing solution from nothing but the reticle and a known target height.
Run it again with a different read to see the sensitivity. If that same 24-inch target measured 2 mils instead, the range would be 24 times 27.8 divided by 2, or about 334 yards, a hundred yards closer. The bigger the target appears in mils, the nearer it is, and small changes in the mil read move the answer a lot, which is the method's main caution.
That is the entire procedure: know the size, measure the mils, apply the formula. With a laminated card of the two formulas and a few common target sizes in your data book, you can range a target in under a minute when the laser is dead.
The weak link is the size estimate
The formula is exact, but it is only as good as the numbers you feed it, and the target size is the biggest source of error. Reticle ranging relies entirely on a correct estimate of the target's true height or width, so a guess that is ten percent off produces a range that is ten percent off, which at distance is a clean miss.3 The math will convert a bad size into a wrong range every time, with no warning that the input was off.
This is why the method depends on known references. Ranging a steel target whose dimensions you recorded, or an object of standard size, is reliable, while ranging a vague natural feature is a guess dressed up as arithmetic. Experienced shooters keep a mental and written library of common sizes, a standard silhouette, a fence post spacing, a window, so they have reliable numbers to work from.
The same care applies to the mil read itself. Measuring to a tenth of a mil takes a steady position and a clear reticle, since a small error in the mil count translates directly into a proportional error in the range.4 Use the largest dimension of the target you can measure cleanly, because the more mils it spans, the less a small reading error matters.
Reading the reticle cleanly
A few practical points make the read trustworthy. A first focal plane scope is what you want for ranging, because its subtensions stay true at every magnification, so a mil reads as a mil whatever power you are on.5 On a second focal plane scope the marks only measure correctly at one magnification, usually maximum, so you must be on that exact power for the formula to work.
Measure carefully against the hash marks, estimating to the nearest tenth of a mil, and use a stable position so the reticle is not dancing on the target. Ranging the taller or wider dimension of the target gives you more mils to measure against, which shrinks the impact of any small reading error and makes the result steadier.
Keep your subtension card handy until the formula is second nature. Manufacturers publish the exact mil values of every mark on their reticles, and knowing yours cold turns the glass into a ruler you can read without hesitation when the clock or the conditions are against you.
What I'd do
I would learn the mil relation formula cold and carry it on a laminated card with a short list of common target sizes, because the one time I need it is the time my laser has already failed. My approach is to range off a known dimension, a steel target height I recorded or a standard object, never a vague guess at a natural feature.
I would run a first focal plane scope so the mils read true at any magnification, measure to a tenth of a mil from a steady position, and use the largest clean dimension of the target to keep small reading errors from blowing up the range. Then I would treat the result as a solid estimate to confirm, not a laser-grade certainty.
The point is not to replace the rangefinder but to never be stranded without one. A mil reticle and a known size are a rangefinder that needs no batteries, and learning to use them is cheap insurance that also makes you better with the reticle every day you do not need it.
FAQ
What is mil reticle ranging?
Mil reticle ranging is estimating distance by measuring how many mils a known-size target covers in your scope's reticle, then solving with the mil relation formula. Because a mil is a fixed fraction of the distance, the apparent size of a known object reveals how far away it is. It is the old-school backup for when a laser rangefinder fails.
What is the mil relation formula?
In metric, range in meters equals target size in meters times one thousand, divided by the size in mils. In imperial, range in yards equals target size in inches times 27.8, divided by the size in mils. Both need only the true target size and the mils it spans in the reticle, and both express the same fixed proportion of the milliradian.
How accurate is reticle ranging compared to a laser?
Reticle ranging is less accurate and slower than a laser, because it depends entirely on your estimate of the target's true size and a careful mil read. A ten percent error in the size produces a ten percent error in the range. Ranging off a known dimension keeps it reliable, but treat the result as a solid estimate to confirm, not laser-grade certainty.
Do I need a first focal plane scope to range with the reticle?
A first focal plane scope is strongly preferred, because its subtensions read true at every magnification, so a mil is always a mil. A second focal plane reticle only measures correctly at one magnification, usually maximum power, so you must be on that exact setting for the mil relation formula to give a correct range.
Citations
- The Shooters Log. (2021). Estimating Range With a Mil-Dot Reticle. The Shooters Log.
- 8541 Tactical. (2019). Mildot Range Estimation. 8541 Tactical.
- Optics Warehouse. (2022). How to Estimate Range Using Your Scope Reticle. Optics Warehouse.
- Sniper Central. (2020). Mastering Mildots. Sniper Central.
- Swampfox Optics. (2023). First Focal Plane vs Second Focal Plane Reticles. Swampfox Optics.