What Do NETD, mK & Sensor Size Mean? Thermal Specs Explained

Here’s the deal: you’ve decided it’s time to take your night hunting to the next level. You start shopping for a thermal scope, and suddenly you are drowning in alphabet soup. You’re seeing terms like "NETD," "mK," "pixel pitch," and sensor resolutions that look like old computer monitor sizes. It’s enough to make you want to close your laptop and stick to hunting in the daylight.

We’ve all been there. Trying to figure out how these technical numbers translate to real-world performance out in the field can be frustrating. But getting a grip on these terms is the secret to getting the right gear without overspending or under-equipping yourself.

In this thermal scope specs explained guide, we’re going to break down all the confusing jargon into plain English. By the time we’re done, you’ll know exactly what you’re looking at and why it matters on the hunt.

What Are Thermal Specs and Why They Matter

A traditional day scope relies on glass and light. A thermal scope doesn't care about light at all. Instead, it reads heat signatures. The ground, the trees, and the feral hog standing in front of them all give off different amounts of thermal energy (heat). Your thermal scope reads those differences and paints a picture on a digital screen.

The specs on a thermal scope tell you exactly how good the device is at picking up those heat differences and how crisp the final image will be. When you understand the numbers, you know exactly what a scope is capable of before you ever mount it to your rifle. This is your ultimate thermal imaging specs guide.

What Is NETD (mK)?

If you’ve ever wondered what is NETD thermal, you’re not alone. NETD stands for Noise Equivalent Temperature Difference. That’s a mouthful of engineering jargon. In plain English, it means thermal sensitivity.

NETD tells you how well the thermal sensor can tell the difference between two objects that are almost the exact same temperature.

Understanding mK (Millikelvin)

NETD is measured in millikelvins, abbreviated as "mK." The most important rule to remember here is: Lower is better.

Think of it like a golf score. A thermal scope with a rating of ≤18mK (like our ThOR 6 Mini) is significantly more sensitive than an older scope with a ≤50mK rating.

Why does lower mK matter in the real world? Imagine you are out hog hunting on a clear, dry night where the air is cool and the hogs are warm. Almost any thermal scope will give you a great image. But what happens when the humidity rolls in, or it starts drizzling, or there's heavy fog? Suddenly, the wet trees, the damp ground, and the air itself start to look like the same temperature.

A scope with a high mK rating (less sensitive) will show you a muddy, gray, washed-out screen. A scope with a low mK rating (highly sensitive) will easily pick through that "thermal noise" and give you a crisp, clear outline of your target, pulling its weight when conditions get tough.

Thermal Sensor Resolution Explained

If NETD is about sensitivity, sensor resolution is about clarity.

When you look at our thermal sensor resolution guide, you’ll usually see numbers like 160x120, 320x240, 640x480, and all the way up to a massive 1280x1024. These numbers represent the amount of pixels on the thermal sensor. Just like a TV screen, more pixels mean a sharper, higher-definition image.

• Entry-Level (e.g., 160x120 or 256x192): Great for close-range work like pest control around the barn. It gets the job done inside 100 yards.
• Mid-Range (e.g., 320x240): The sweet spot for most hunters. It gives you a great image and lets you confidently identify a coyote or a hog out to a couple hundred yards.
• High-End (e.g., 640x480 or 1280x1024): This is where you get incredible detail. More pixels mean you can use your digital zoom without the image immediately turning into a blocky, pixelated mess. If you're hunting wide-open spaces where you need to identify a target at 400+ yards, you want a higher resolution.

Why Sensor Size and Pixel Pitch Matter

You’ll also see specs talking about "12µm" (microns). This is the pixel pitch—literally how close together the pixels are packed on the sensor.

Older thermals used 17µm sensors. Today, standard ATN thermals use a smaller, more advanced 12µm pitch. Why does this matter? A smaller pixel pitch allows for higher magnification and longer detection ranges without needing a giant, heavy lens. It’s the reason modern thermal scopes punch above their weight, giving you massive performance in a lightweight package.

How These Specs Work Together

You can't look at just one spec in a vacuum. A scope's performance is a combination of its NETD sensitivity, sensor resolution, and lens size.

If you have a massive 640x480 resolution but a terrible NETD rating, your image will be high-definition, but washed out in humid weather. If you have an amazing NETD rating but low resolution, the image will have great contrast, but you won't be able to zoom in very far.

When you combine a low NETD (like ≤18mK) with a high resolution (like 640x480) and a quality lens, you get a game-changer of a scope. You get massive detection ranges (often 3,000+ yards) and the ability to not just see heat, but to clearly identify whether that heat signature is a coyote, a calf, or your neighbor’s dog.

The ATN Thermal Lineup Overview

At ATN, we build thermals for every type of hunter. Let's look at how these specs play out across our lineup:

• ATN ThOR LTV: This is our ultra-lightweight, easy-to-use option. It features 160, 256, 320, and 640 sensor options. It skips the complex smart features in favor of pure, simple performance and a fast One Shot Zero. It earns its keep for hunters who just want to mount a scope and get to work.
• ATN ThOR 4: The workhorse. Featuring Gen 4 sensors (384 or 640 resolution) and smart features like a built-in Ballistic Calculator, Recoil Activated Video (RAV), and a 16+ hour battery life. It's built for serious field use.
• ATN ThOR 5 & ThOR 6 Mini: The cutting edge. These scopes feature improved image processing, optional built-in Laser Rangefinders (on the ThOR 5), and incredibly sensitive sensors. The ThOR 6 Mini boasts an ultra-low ≤18mK NETD rating, meaning it cuts through rain and fog like a hot knife through butter.
• ATN ThOR XD: For those who absolutely refuse to compromise, this model features a true 1280 thermal sensor—the highest resolution in the industry—giving you the clearest, crispest thermal image money can buy.

How to Choose a Thermal Scope

Figuring out how to choose a thermal scope comes down to matching the specs to your specific hunt.

• Baiting hogs at 75 yards? You don’t need a 640 sensor. An entry-to-mid-level ThOR LTV with a 256 or 320 sensor will easily get the job done and save you some cash.
• Calling coyotes across wide-open pastures? You need range and clarity. Step up to a ThOR 4 or ThOR 5 with a 640 sensor so you can confidently zoom in and identify a predator at 300 yards before pulling the trigger.
• Hunting in the humid swamps of the South? Prioritize a low NETD rating. Look closely at the ThOR 6 Mini’s ≤18mK sensitivity so the summer humidity doesn't ruin your image quality.

The Bottom Line

Thermal specs don't have to be intimidating. Resolution tells you how clear and detailed the image is, and NETD (mK) tells you how well the scope performs when the weather gets nasty. Combine those two numbers, and you'll know exactly what a piece of glass is capable of in the field.

If you’re ready to own the night, ATN has a scope built for your rifle, your hunt, and your budget. Stop guessing in the dark and step up to gear that actually earns its keep.

Ready to find your perfect thermal? Shop the full line of ATN Thermal Scopes here and change the way you hunt forever.

Quick Reference: Thermal Specs Cheat Sheet

• NETD (Thermal Sensitivity): Measured in mK. Lower is better. (e.g., 18mK is vastly superior to 50mK, especially in fog/rain).
• Sensor Resolution: Measured in pixels. Higher is better for detail and zooming. (e.g., 640x480 gives you double the baseline clarity of 320x240).
• Pixel Pitch: Measured in µm (microns). Lower is better for magnification. Modern standard is 12µm.
• Detection Range: The distance you can tell something warm is out there.
• Identification Range: The distance you can tell exactly what that warm thing is (e.g., a hog vs. a deer).