Thermal detection range calculator
Pick a monocular or type a lens and pixel pitch, choose a target, and get the distances to detect, recognize and identify it.
How far it sees
19 mm ÷ 12 µm = 1,583 pixels per radian. Horizontal field: 13.8° on a 384×288 sensor.
- Detection, 1,425 m (1,558 yd): something warm is there (2 px on target).
- Recognition, 356 m (389 yd): what kind of animal it is (8 px on target).
- Identification, 219 m (240 yd): which one: buck or doe, dog or coyote (13 px on target).
Lens and pixel pitch from the makers' figures read on November 9, 2026; thresholds from the Johnson criteria. Best case for a clear night. Our methodology · Comparison tool
How the numbers are worked out
A pixel on the sensor covers a small angle: pixel pitch divided by focal length. A target of a given size covers more pixels when it is closer. The distance at which it covers N pixels is focal length ÷ pixel pitch × target size ÷ N. That is all the calculator does.
The pixel thresholds come from John Johnson's 1958 criteria, still used in thermal spec sheets: about 2 pixels (one line pair) to detect, 8 pixels to recognize the type of target and 13 pixels to identify it, each with roughly even odds. The score on our rankings uses a "reach" at 3 pixels on a 1.8 m target, a slightly stricter detection that lands on the same figures Pulsar and AGM publish for their 12 µm models.
What the formula cannot know: the weather, the humidity, how warm the animal is against the ground, and the image processing of each brand. On a muggy summer night in Georgia you will get less; on a dry January night in Montana, more.
Distances for every monocular we compare
Person standing (1.8 m), from the lens and pixel pitch published by each brand (read November 9, 2026). Sorted from the longest reach.
| Monocular | Lens / pitch | Detect | Recognize | Identify |
|---|---|---|---|---|
| Pulsar Telos LRF XP50 | 50 mm / 17 µm | 2,647 m | 662 m | 407 m |
| Nocpix Vista H35R | 35 mm / 12 µm | 2,625 m | 656 m | 404 m |
| Pulsar Axion 2 LRF XG35 | 35 mm / 12 µm | 2,625 m | 656 m | 404 m |
| Pulsar Axion 2 XG35 | 35 mm / 12 µm | 2,625 m | 656 m | 404 m |
| Burris BTH35 v3 | 35 mm / 12 µm | 2,625 m | 656 m | 404 m |
| AGM ReachIR LRF 25-384 | 25 mm / 12 µm | 1,875 m | 469 m | 288 m |
| Vortex Veil 400 | 25 mm / 12 µm | 1,875 m | 469 m | 288 m |
| ATN OTS LT 320 3-6x | 25 mm / 12 µm | 1,875 m | 469 m | 288 m |
| AGM Taipan V2 19-384 | 19 mm / 12 µm | 1,425 m | 356 m | 219 m |
| TOPDON TS004 Pro | 19 mm / 12 µm | 1,425 m | 356 m | 219 m |
| RIX Pocket K3 | 15 mm / 12 µm | 1,125 m | 281 m | 173 m |
| Pulsar Axion XQ19 Compact | 19 mm / 17 µm | 1,006 m | 251 m | 155 m |
| TOPDON TS004 | 13 mm / 12 µm | 975 m | 244 m | 150 m |
| AGM Taipan V2 10-256 | 10 mm / 12 µm | 750 m | 188 m | 115 m |
Frequently asked questions
How far can a thermal monocular see?
Far enough to detect a person-sized heat source at 750 to 2,647 m with the models we compare (Johnson detection, 2 pixels on 1.8 m). Telling what the animal is takes four times closer, and naming it (buck or doe) about six times closer. Our [guide to thermal range](/guides/how-far-can-thermal-see/) explains why.
Why is the brand range longer than recognition?
Brands quote detection, the easiest level: a few warm pixels in the frame. You will usually want to recognize an animal before you act, which happens at a quarter of that distance or less.
Does a higher resolution sensor see farther?
Not by itself. Distance depends on focal length divided by pixel pitch. A 640 sensor and a 384 sensor with the same lens and pixel size see the same distance; the 640 shows a wider field. Resolution matters for detail and for digital zoom.
How accurate is this calculator?
It is geometry, the same method spec sheets use. Real range is shorter in rain, fog, high humidity or when the animal is barely warmer than the background, and longer on a cold, dry night. Treat the numbers as the best case for a clear night.