How to Read Rifle Scope Numbers: What 4-16x40 Means (2026)
You are comparing scopes and every product name is a string of numbers — 3-9x40, 4-16x40, 1-6x24, 2.5-20x50 — with no explanation of what any of it means. The code is simpler than it looks. The numbers before the "x" are the magnification range, and the number after the "x" is the objective lens diameter in millimeters — so 4-16x40 is a scope that zooms from 4× to 16× through a 40 mm objective lens. Once you can read that, you can tell at a glance whether a scope fits your shooting.
Key takeaways
- The number (or range) before the "x" is magnification — how many times closer the target appears. A range like 4-16 means a variable scope; a single number like 6 means fixed power.
- The number after the "x" is the objective lens diameter in millimeters. A larger objective gathers more light, which helps in low light, but it adds weight and sits higher on the rifle.
- More magnification is not automatically better — it narrows your field of view, magnifies mirage and wobble, and shrinks the forgiving zone behind the scope.
- Match the numbers to your distance: a 1-6x24 for close and fast, a 4-16x40 for mid-to-long range, a 2.5-20x50 like the Accufire EVRO-12 for versatility from brush to distance.
The numbers before the "x": magnification
Magnification is how much larger the target looks through the scope than it does to your naked eye. A 4× setting makes a target appear four times closer. When you see two numbers joined by a dash — 4-16 — the scope is variable, and you can dial anywhere between the low and high power with a zoom ring. A single number, like 6x42, means a fixed-power scope locked at one magnification. Variable scopes are the most common choice today because one optic covers a close shot at low power and a distant one zoomed in.
The number after the "x": objective lens diameter
The final number is the diameter of the front (objective) lens in millimeters — the 40 in 4-16x40. That lens is the scope's window onto the world, and its size controls how much light it can gather. A bigger objective delivers a brighter image, which matters most at dawn, dusk, and high magnification where light gets scarce. The trade-off is physical: a 50 mm or 56 mm objective is heavier, bulkier, and has to be mounted in higher rings to clear the barrel, which raises your line of sight over the bore.
Choosing magnification by use case
Read the numbers against the distance you actually shoot. For close-quarters and fast target work, a low-range variable like a 1-6x24 lets you keep both eyes open at 1× and still reach out at 6×. General hunting is well served by a classic 3-9x40. Mid-to-long-range and varmint shooting lean on something like a 4-16x40, and precision shooters who want one scope to do everything reach for a wide-range optic such as a 2.5-20x50. There is no single "best" set of numbers — only the set that matches your rifle's job.
| Scope marking | Magnification | Objective | Best suited to |
|---|---|---|---|
| 1-6x24 | 1–6× variable | 24 mm | Close to mid range; both eyes open at 1× |
| 3-9x40 | 3–9× variable | 40 mm | All-around hunting |
| 4-16x40 | 4–16× variable | 40 mm | Mid-to-long range and varmint |
| 2.5-20x50 | 2.5–20× variable | 50 mm | Versatile precision (e.g., Accufire EVRO-12, ATRO-20) |
Does a bigger objective mean a better scope?
Not on its own. Beyond a certain point the extra light a large objective gathers exceeds what your eye can use, especially in daylight, so a 56 mm lens is not twice as good as a 40 mm. What you gain in brightness you pay for in weight, bulk, and a higher mounting position that can hurt your cheek weld. Glass quality, coatings, and the scope's mechanical tracking usually matter more to real-world performance than chasing the largest front lens.
Reading the rest of the spec sheet
Two more numbers round out most listings. Tube diameter — commonly 1 inch or 30 mm — affects how much elevation adjustment the scope has and which rings it needs; the Accufire EVRO-12 and ATRO-20 both use a 30 mm tube. You will also see whether the reticle sits in the first or second focal plane, which changes how its holdover marks behave as you zoom. If that distinction is new, our guide to the first vs second focal plane breaks it down.
Now that the numbers make sense, match them to your build. Accufire's rifle scopes pair a wide magnification range with a 30 mm tube and side-focus parallax — explore Accufire rifle scopes.
Accufire EVRO-12 Essential Variable Rifle Scope — $479.00. A 2.5–20x50 first focal plane optic: 2.5× to 20× magnification through a 50 mm objective, on a 30 mm tube with side-focus parallax and 0.1-mil turrets. View the EVRO-12.
Frequently asked questions
What does 4-16x40 mean on a scope?
The 4-16 is the variable magnification range, meaning the scope adjusts from 4 times to 16 times magnification. The 40 is the objective lens diameter in millimeters, which controls how much light the scope gathers.
What do the two numbers before the x mean?
They are the magnification range, from the lowest power to the highest power the scope can dial to. If there is only a single number before the x, the scope is fixed at that one magnification instead of being variable.
What does the number after the x mean?
It is the diameter of the objective lens in millimeters. A larger objective gathers more light for a brighter image in low light, but it also makes the scope heavier and forces a higher mounting position over the barrel.
Is higher magnification always better?
No. More magnification narrows your field of view, makes mirage and natural wobble more obvious, and adds weight, so it can actually be harder to use up close. The right magnification matches the distance you shoot most.
What magnification does the Accufire EVRO-12 have?
The Accufire EVRO-12 is a 2.5-20x50 scope, which means it has a variable magnification range of 2.5 times to 20 times and a 50 millimeter objective lens.
Decoding the numbers is the first step in choosing a scope; the next is matching magnification format and reticle to your distance. Our comparison of an LPVO vs a fixed-power scope and our guide to how to zero a rifle scope cover the next decisions once your optic is on the rifle.