NETD sits on almost every thermal camera spec sheet and rarely gets explained. It is worth understanding, because it affects how much subtle detail you can see.
The definition
NETD stands for noise equivalent temperature difference. It is the smallest temperature difference a camera can distinguish from its own electronic noise, and it is measured in millikelvin (mK). A figure of 40mK means the camera can show differences of about 0.04°C (0.07°F).
Lower is better
A lower NETD means the image is cleaner and can reveal fainter differences, such as a slightly damp patch of wall or a connection running a little warmer than its neighbors. A higher NETD gives a noisier, flatter image where subtle patterns disappear.
What is good enough?
- Around 50mK or lower: solid for general inspection, home energy checks and electrical work.
- Around 40mK or lower: better for finding subtle moisture and insulation issues, and for professional reports.
- Above about 60mK: fine for obvious problems, but expect less fine detail.
NETD is not the whole story
NETD is measured under controlled conditions, and manufacturers do not all test the same way. Treat it as one input alongside resolution, lens and frame rate. A high-resolution camera with poor NETD can still produce a noisy image, and a low NETD cannot make up for too few pixels.
Conditions matter too
Real-world sensitivity also depends on the scene. Subtle problems show up best when there is a decent temperature difference between inside and outside, or when the equipment is under load. See how to run a home energy audit for conditions that help.
For how NETD fits with other specs, read the buyer's guide.