How do I calculate the right lens focal length for a CCTV camera?

Focal length depends on three things: how far the target is, what camera resolution you have, and what DORI grade you need (Detect / Observe / Recognise / Identify per EN 62676-4). The formula is focal_mm = distance_m × sensor_width_mm / coverage_width_m, where coverage_width = horizontal_pixels / required_pixels-per-metre. For a 5 MP camera at 15 m needing Identify (250 px/m), the coverage width is 12.3 m, so on a 1/2.8" sensor (5.4 mm wide) you need about 6.6 mm focal length — round up to a popular value like 8 mm.

What is DORI and which grade do I pick?

DORI stands for Detection / Observation / Recognition / Identification — the four pixel-density grades defined by EN 62676-4. Detect (25 px/m): you can see a person is there. Observe (62.5 px/m): you can describe what they're doing. Recognise (125 px/m): you can match them against a known list. Identify (250 px/m): you can identify a stranger from the footage. Most insurance and EU GDPR cases require Recognise or Identify on entry points.

Why does my chosen lens cover less than my expected area?

Three reasons. (1) Sensor format: a 1/3" sensor is narrower than a 1/2.8", so the same focal length gives a narrower field of view. (2) Aspect ratio: 16:9 sensors crop the vertical, giving smaller vertical coverage than 4:3. (3) Lens distortion: wide-angle lenses (under 4 mm) lose effective pixels at the edges. Always cross-check the manufacturer's published HFOV against your calculation.

Is one lens enough for the whole scene, or do I need multiple cameras?

Depends on the scene depth. A single fixed lens gives the required pixel density at exactly one distance — everything closer is over-resolved, everything further is under-resolved. For mixed-depth scenes (long corridor, large parking lot, retail floor), use either (a) a varifocal lens you tune at install time, (b) a multi-sensor 360° camera that covers different zones with different sensors, or (c) two cameras: wide for overview + telephoto for the critical detection zone.

How does CCTVplanner's lens calculator compare to JVSG's?

Both use the same EN 62676-4 DORI math. The big differences: CCTVplanner runs in any browser with no install (JVSG is Windows-only at higher tiers), is free at our entry tier (JVSG is paid-only at €350+), and reads the lens calculation back into a full project designer where you can drop the camera on a map, add fences and obstacles, and export a CAD-grade DXF — JVSG keeps the lens calculator as a standalone, not integrated into the design flow.

Does the calculator account for fisheye or wide-angle distortion?

The basic focal-length calculation assumes a rectilinear lens (most cameras 2.8 mm and above). For fisheye lenses (1.0–1.8 mm) the geometry is non-linear and the effective pixel density falls off sharply away from the centre. For fisheye install design, use the full CCTVplanner designer which applies the camera's actual lens distortion model from the datasheet, not a generic cone.

CCTV Lens Calculator — Pick the Right Focal Length

Enter your target distance, camera resolution, and the DORI grade you need (Detect / Observe / Recognise / Identify) — get the right focal length in millimetres. Free, browser-only, no signup.

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Target distance: 15 m

DORI grade (EN 62676-4)

identify a stranger

Camera resolution

Recommended lens

Focal length needed

8 mm

Exact requirement: 6.59 mm. Nearest popular size: 8 mm.

Coverage at the target distance

10.1 m wide → 303 px/m

Meets the Identify grade (250 px/m). Computed for a 1/2.8" sensor (5.4 mm).

Why use CCTVplanner's lens calculator

• EN 62676-4 DORI grades built-in. Pick Detect / Observe / Recognise / Identify directly. No memorising px/m thresholds.
• Browser-only, no install. Works on Chromebook, iPad and any phone. JVSG's lens calculator requires their Windows install at higher tiers.
• Reads back into the full designer. Drop the recommended camera onto a satellite map, project the cone over your actual site, add fences, obstacles, and export a CAD-grade DXF + BoM.
• 65,000+ verified cameras. Once you know the focal length, pick from the catalog — we apply each camera's actual sensor and lens specs, not a generic cone.

Related tools

Advanced lens selector →

Sensor format selector, tilt angle, multi-zone comparison

FOV calculator →

Reverse: from focal length to field of view

DORI zone calculator →

Plot Detect/Observe/Recognise/Identify rings for a chosen lens

Take the lens into a full design

Drop the recommended camera onto a real satellite map and check coverage against your site — free, no signup needed.