How this is worked out
- Field of view comes from the lens and the sensor: angle = 2 × arctan(sensor width ÷ (2 × focal length)).
- Scene width at a distance = 2 × distance × tan(half the angle). Double the distance and you cover double the width — at half the detail.
- Pixel density is the camera’s horizontal pixels divided by the scene width, in pixels per metre. This, not the megapixels alone, decides what you can prove on camera.
- DORI (IEC 62676-4) sets the thresholds: Detect 25 px/m, Observe 62.5 px/m, Recognise 125 px/m, Identify 250 px/m.
- For a number plate, aim for 150–200 px/m across the plate and keep the angle under about 30° to the direction of travel.
An estimate for planning, not a design document. Site conditions change the answer — send it to us and we will confirm it free of charge.