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Camera Field of View Calculator
Work out a camera's horizontal field of view, the scene width at a given distance, and whether the resulting pixel density is enough to identify a face or read a plate — using the same Johnson's Criteria thresholds manufacturers publish on their own lens calculators.
Camera & lens
Field of view
How this calculator works
Focal length and sensor size alone only tell you the angle of view — they don't tell you whether the camera is actually useful at the distance you're placing it. A wide lens covering a whole parking lot is worthless for identification if every face is compressed into a handful of pixels. That's why this calculator carries the field of view all the way through to pixel density at your chosen distance, not just the angle.
Johnson's Criteria: what the pixel density actually means
Johnson's Criteria is the standard used across the security industry — including by Axis, Bosch, Hikvision, and Dahua's own lens calculators — to translate a raw pixel-density number into a real-world capability. It defines three practical thresholds:
| Classification | Pixel density | What it means in practice |
|---|---|---|
| Identification | ≥ 125 px/m | Enough detail to confirm who a person is, or read a plate |
| Recognition | ≥ 63 px/m | Enough to recognize a familiar face or vehicle type |
| Detection | ≥ 25 px/m | Enough to notice that a person or vehicle is present |
Below 25 px/m, footage is generally only good for general scene monitoring — not for picking out detail after the fact. These thresholds are why a camera spec sheet's megapixel count means very little on its own: the same sensor and lens gives identification-grade detail at the doorway and barely detection-grade detail at the far end of a parking lot.
Real-world caveats
This calculator gives the geometric ideal — it doesn't account for lens distortion (especially at the edges of wide-angle lenses), video compression artifacts, low light or backlight conditions, or a subject that isn't facing the camera. Treat the pixel-density numbers as a best-case ceiling, and add margin for anything mission-critical like a license-plate-capture point or a controlled entry.
Related tools & guides
Not sure how to pick the lens in the first place, or why a wider field of view can leave everyone in it unidentifiable? See Choosing the Right CCTV Lens: Coverage vs. Identification Distance.
Once you've confirmed the coverage a camera gives you, check whether your network can carry it — use the IP Camera Bandwidth Calculator to size the total bitrate and uplink, and see IP Camera Bandwidth: Why the Switch (and PoE Budget) Fail Before the Network Does for the two mistakes that break installs even when bandwidth looks fine.
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