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Guide

How to Compare Thermal Camera Resolution

Two cameras claim 320×240 and 240×240. One has 76,800 detector elements; the other has 16,384 upscaled. The spec sheets look similar until you know which line to read and how to turn it into millimeters at the distance you work.

By the Akermin Editorial Team · 3 min read

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Compare thermal cameras on native detector resolution only, found on the spec sheet as “IR resolution” or “detector” (e.g. 160×120, 256×192, 320×240). Disregard super-resolution, display and visible-camera figures. Then compute the pixel patch at your working distance: patch = distance × field of view (radians) ÷ pixels across. A target must span about three pixels for an accurate temperature, so the smallest measurable feature is three patches. That single calculation ranks any two cameras for your use.

Step 1: Find the native figure

Spec sheet term Is it native?
IR resolution, detector resolution, thermal resolution Yes
Super-resolution, TISR, VividIR, UltraMax, enhanced No; upscaled from the native figure
Display resolution, screen resolution No; the LCD
Visual camera, digital camera megapixels No; the visible camera for overlays
Pixels (e.g. 19,200 pixels) Yes if it equals width × height of the native array

If a listing gives only an upscaled figure, halve each dimension as a rough guess and look for the datasheet.

Step 2: Compute the pixel patch

IFOV (instantaneous field of view) per pixel = horizontal field of view ÷ horizontal pixels. Convert degrees to radians (× 0.01745). Patch at distance D = D × IFOV.

Camera Native HFOV IFOV (mrad) Patch at 3 m Smallest measurable at 3 m (3 px)
Entry phone dongle 80×60 50° 10.9 33 mm 98 mm
FLIR One Pro / C5 160×120 54° 5.9 18 mm 53 mm
TOPDON TC001 series 256×192 56° 3.8 11 mm 34 mm
FLIR C8 / E8 320×240 54° 2.9 9 mm 27 mm
Professional 640×480 42° 1.1 3.4 mm 10 mm

A narrower lens shrinks the patch at the cost of coverage; a 24° lens halves the numbers above.

Step 3: Apply the three-pixel rule

A target smaller than about three pixels across is blended with its surroundings and its temperature reads toward the background. For seeing that something exists, one to two pixels suffice; for measuring its temperature, three or more. Electrical terminals of 10 mm from 2 m therefore need 320×240 or a telephoto lens; a 300 mm insulation gap from 3 m is fine on 80×60.

Step 4: Trade against sensitivity and cost

Higher resolution at the same price often comes with worse NETD or fewer features. For building work, where contrasts are small and targets large, a 160×120 camera with 40 mK can outperform a 320×240 camera with 100 mK. Check both. See how to understand NETD and thermal sensitivity.

Worked comparison

Camera A: 240×240 “TISR”, native 128×128, 40° lens, 60 mK. Camera B: 160×120 native, 54° lens, 70 mK. At 3 m: A’s patch = 3 × (0.698 ÷ 128) = 16 mm; B’s = 3 × (0.942 ÷ 160) = 18 mm. Nearly equal despite the headline numbers, and A has slightly better sensitivity. The upscaled 240 figure was irrelevant.

Distance in practice

Rather than buying resolution, stand closer where you can. Halving the distance halves the patch. Resolution buys the ability to work from further away, which matters for electrical (safety) and roofs and facades (access). Cameras are compared by native resolution in best thermal cameras for home inspection; background in thermal camera resolution explained.

Flir C5 Compact Thermal Imaging Camera, WiFi, 160x120 MSX, Ignite

Flir C5 Compact Thermal Imaging Camera, WiFi, 160x120 MSX, Ignite

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Flir C8 Compact Thermal Imaging Camera, 320x240 MSX, Ignite Cloud

Flir C8 Compact Thermal Imaging Camera, 320x240 MSX, Ignite Cloud

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TOPDON TC004 Mini Thermal Imaging Camera, 240 x 240 TISR Resolution

TOPDON TC004 Mini Thermal Imaging Camera, 240 x 240 TISR

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Products shown because their documented specifications fit this guide. Price and availability are on Amazon and can change.

Frequently Asked Questions

How do I calculate the size a thermal camera can resolve?

Pixel patch = distance × (horizontal field of view in radians ÷ horizontal pixels). A 160×120 camera with a 50° lens at 3 m sees patches of about 16 mm; a reliable measurement needs a target three times that, about 50 mm.

Is 256×192 much better than 160×120?

It has 2.5 times the pixels and resolves features about 1.6 times smaller at the same distance, or the same features from 1.6 times further away. It is a noticeable step.

What is spot-size ratio?

The distance at which a pixel (or the measurement spot) covers one unit of target size, e.g. 150:1 means a 10 mm target is one pixel at 1.5 m. Higher is better for measuring small things at distance.

Affiliate disclosure: Akermin earns a commission from qualifying Amazon purchases made through links on this page. Our editorial picks are based on documented specifications and owner feedback, not commissions.