Free tool · UK
CCTV lens calculator
Pick the right lens before the ladder comes out: field of view, scene width and pixels-per-metre at your distance, verdicted against the DORI identification thresholds.
Field of view
85°
horizontal angle
Scene width at 10m
18.2 m
what the frame covers
Detail level
141 ppm
Recognise: can recognise someone you know; read a plate
| DORI level | Needs | This setup |
|---|---|---|
| Identify | ≥ 250 ppm | up to ~5.6 m |
| Recognise | ≥ 125 ppm | Yes |
| Observe | ≥ 62 ppm | Yes |
| Detect | ≥ 25 ppm | Yes |
Cameras we hold at 2.8 mm
- 2.8 mm fixed2MP HD 4in1 Dome Camera (2.8mm/ White)£13.79
- 2.8 mm fixedProlux 4MP PoC Audio Eyeball Camera 2.8mm 50m IR Hikvision Compatible£24.67
- 2.8 mm fixedHikvision 5 MP PIR Fixed Turret Camera£28.65
- 2.8 mm fixedHikvision 5 MP Audio Fixed Turret Camera£29.84
- 2.8 mm fixedHikvision 5 MP Audio Fixed Turret Camera£30.92
- 2.8 mm fixedVIPER PRO 5MP 3K ColorVu Camera - 24-Hour Smart Light CCTV£36.79
The figures above assume the sensor you picked. Check the camera's own sensor size on its page — a wider sensor gives a wider view at the same focal length.
Reading the result
A wide lens (2.8mm) sees a lot and identifies little; a telephoto (12mm) identifies at distance through a keyhole. The DORI thresholds (IEC 62676-4) turn that trade-off into numbers: 250 pixels per metre to identify a stranger, 125 to recognise someone you know or read a plate, 62 to observe what happened, 25 to detect movement.
The practical pattern: a wide lens at the door for context, and a tighter lens (or a higher-resolution camera) on the approach path where identification matters. Where one camera must do both jobs, a varifocal model lets you set the compromise on site.