When to use: Select the right lens focal length for a camera by computing the horizontal, vertical, and diagonal field of view from the lens focal length and the imager (sensor) size. FOV = 2·atan(sensor / (2·f)). The coverage width at the target distance and the resulting pixel density determine whether a scene supports Detect, Observe, Recognize, or Identify per the EN 62676-4 DORI criteria.
This calculator computes the horizontal, vertical, and diagonal field of view for any camera lens and sensor format combination, then determines coverage width at a target distance and pixel density for DORI classification. Engineers use it to select the correct focal length lens for a specific surveillance task.
Field of view is derived from the optical formula FOV = 2 × arctan(sensor_dimension / (2 × focal_length)). The horizontal FOV uses the sensor width, vertical FOV uses the sensor height, and diagonal FOV uses the diagonal sensor dimension. Shorter focal lengths produce wider angles; longer focal lengths produce narrower, telephoto views.
Coverage width at a given distance is: Width = 2 × Distance × tan(HFOV / 2). Pixel density at that distance is horizontal pixel count divided by coverage width in feet, then converted to pixels per meter. Pixel density directly determines which EN 62676-4 DORI level (Detection 25, Observation 62.5, Recognition 125, or Identification 250 px/m) the camera achieves at that range.
Sensor format conventions use the optical format designation (1/3", 1/2.8", 1/2", 1" etc.) which corresponds to specific active imager dimensions in millimeters. A larger sensor format with the same focal length always produces a wider field of view.
EN 62676-4 (IEC 62676-4) defines the DORI pixel density thresholds used to classify camera performance at a scene: Detection at 25 px/m is sufficient to detect a human presence; Observation at 62.5 px/m allows behavioral assessment; Recognition at 125 px/m allows identification of a known person; Identification at 250 px/m allows identification of an unknown individual. These thresholds are widely adopted in physical security specifications worldwide and referenced in IPVM design standards. ONVIF profiles specify minimum image quality requirements that align with these DORI levels.
The pixel density calculation assumes the camera is pointing perpendicular to the target plane at the stated distance; oblique camera angles reduce effective pixel density. Mounting height, tilt, and lens distortion all affect real-world performance relative to the theoretical FOV calculation.
Select a focal length that achieves the required DORI level at the maximum target distance, not just the nominal distance, to ensure consistent performance. Varifocal lenses provide installation flexibility but the narrowest field of view (telephoto end) should be checked to confirm adequate coverage width.
Select the camera sensor format from the dropdown, enter the focal length in millimeters, the target distance in feet, and the horizontal pixel count of the camera (e.g. 1920 for 1080p, 2560 for 4MP, 3840 for 4K). The calculator immediately shows horizontal, vertical, and diagonal FOV in degrees, coverage width and height at the entered distance, pixel density in px/ft and px/m, and the resulting DORI level. Adjust the focal length to find the lens that achieves the required DORI level at your maximum target distance.
For identification (250 px/m) at 30 feet with a 1080p (1920 px horizontal) camera and a 1/2.8" sensor, you need a focal length of approximately 8–12 mm. Use this calculator with your specific sensor size and resolution to find the exact focal length.
Recognition (125 px/m) allows a viewer to confirm whether a known person is the individual in the frame — it is suitable for access verification. Identification (250 px/m) provides sufficient detail to identify an unknown individual and is required for evidential purposes such as prosecution.
Not necessarily. DORI level depends on pixel density across the scene — both megapixel count and coverage width matter. A 4MP camera with a narrow field of view covering a 10-foot width will outperform an 8MP camera with a wide angle covering 60 feet at the same distance.
A larger sensor produces a wider FOV for the same focal length. A 1" sensor with a 4 mm lens gives a much wider view than a 1/3" sensor with the same lens. Manufacturers specify the optical format (1/3", 1/2.8", 1/2", etc.) which determines the active imager dimensions.
With a 1/2.8" sensor, 12 mm focal length, and 4MP resolution (approximately 2560 horizontal pixels), the calculator will show the coverage width and resulting px/m at any distance. Recognition requires 125 px/m — enter your distance and check if the px/m value meets or exceeds 125.
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