CCTV Field of View (FOV) Calculator
A camera's field of view determines what it can actually see — and at what pixel density. Enter sensor size and focal length to compute horizontal FOV, vertical FOV, scene width at any distance, and the resulting pixel density that maps to DORI tiers per IEC 62676-4. All formulas derived from first-principles pinhole optics.
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The HFOV Formula
Horizontal field of view is fixed by the sensor width and the lens focal length. It is the angle subtended across the horizontal axis of the sensor at the optical centre of the lens:
Where sensor_width is the physical width of the image sensor in millimetres, and f is the focal length of the lens in the same unit. The result is in radians; multiply by 180/π to convert to degrees.
Vertical FOV
The same relationship holds vertically, using the sensor height instead:
For 16:9 sensors, VFOV ≈ HFOV × 9/16. For 4:3 sensors, VFOV ≈ HFOV × 3/4. The diagonal FOV follows the same formula with the diagonal sensor dimension, but horizontal and vertical are almost always the values used in layout design.
Scene Width at Distance
Given an HFOV, the horizontal width of the visible scene at distance d metres is a simple right-angle trigonometry derivation:
Similarly, the scene height is H(d) = 2 · d · tan( VFOV / 2 ). Together, these give the full frame dimensions at any range — the foundation for all coverage planning.
Pixel Density at Distance (PD(d))
Pixel density is the number of horizontal pixels spread across the scene width. It determines what the camera can actually resolve at range and is the input to the DORI model:
A camera with 1920 px horizontal resolution and 90° HFOV produces a scene width of 30 m at 15 m distance, yielding 64 px/m — just past the Observation tier. To achieve Identification-grade density (250 px/m) at the same distance requires either a narrower lens or higher resolution.
Standard Sensor Formats
The same focal length produces a different HFOV on different sensor formats, because the physical sensor width varies. This table lists the most common CCTV sensor formats and their dimensions:
| Format | Width (mm) | Height (mm) | Diagonal (mm) | Typical Resolutions |
|---|---|---|---|---|
| 1/4" | 3.2 | 2.4 | 4.0 | VGA, 720p |
| 1/3" | 4.8 | 3.6 | 6.0 | 720p, 1080p |
| 1/2.7" | 5.3 | 4.0 | 6.6 | 1080p, 3MP |
| 1/2.8" | 5.1 | 3.8 | 6.4 | 1080p, 4MP |
| 1/2.5" | 5.8 | 4.3 | 7.2 | 2MP, 4MP |
| 1/2" | 6.4 | 4.8 | 8.0 | 4MP, 5MP |
| 1/1.8" | 7.2 | 5.3 | 8.9 | 4MP, 8MP (4K) |
| 2/3" | 8.8 | 6.6 | 11.0 | 5MP, 8MP |
A 3.6 mm lens on a 1/2.8" sensor yields ~85° HFOV; the same lens on a 1/1.8" sensor gives ~58°. Always pair focal length with sensor format.
DORI Zones from FOV and Resolution
The DORI model maps pixel density to four surveillance tiers. Given a camera's H_res and HFOV, you can compute the maximum distance for each tier by inverting the PD(d) formula:
| Tier | Min px/m | Max d (1920px, 90°) | Max d (1920px, 60°) | Max d (3840px, 90°) |
|---|---|---|---|---|
| Detection | 25 | 38.4 m | 66.5 m | 76.8 m |
| Observation | 63 | 15.2 m | 26.4 m | 30.5 m |
| Recognition | 125 | 7.7 m | 13.3 m | 15.4 m |
| Identification | 250 | 3.8 m | 6.7 m | 7.7 m |
These are idealised figures. Real range is shorter due to lens distortion, low light, compression, and motion blur. Always design with margin.
Worked Example
Suppose you are designing coverage for a 20 m warehouse corridor. The requirement is Recognition-grade (125 px/m) along its full length, using a camera with 2560 px horizontal resolution and a 1/2.8" sensor (5.1 mm wide).
2. Required focal length: f = sensor_width / (2 · tan(HFOV/2)) = 5.1 / (2 · 0.512) ≈ 4.98 mm
3. A standard 5 mm lens would deliver just under 54° HFOV — meeting the Recognition tier at 20 m.
Inverse: Find Focal Length for a Target Coverage
In practice you often start from a requirement — "I need 125 px/m at 30 metres" — and work backwards to find the lens specification.
2. Required focal length = sensor_width / ( 2 · tan( Target HFOV / 2 ) )
For a 1/2.8" sensor (5.1 mm), 1920 px, 125 px/m at 30 m: Target HFOV = 2 · arctan(1920 / (2 · 30 · 125)) = 2 · arctan(0.256) ≈ 29.0°. f = 5.1 / (2 · tan(14.5°)) ≈ 9.9 mm — a standard 10 mm lens.
Who Uses FOV Calculations?
Security Integrators
Specify camera and lens combinations for each zone, ensuring the required DORI tier is met at every critical distance on the floor plan.
Consultants
Validate designs against IEC 62676-4, produce auditable coverage reports, and compare alternative layouts with objective metrics.
Facility Managers
Verify that existing installations meet current security requirements and plan camera additions for expanding sites.
Analytics Engineers
Ensure pixel density at detection zones meets the minimum thresholds required by AI/ML video analytics for reliable event detection.
The free CCTV Design Tool computes FOV, pixel density, and DORI bands from the configured camera resolution, sensor, and lens data. Drag a camera onto a calibrated plan and review the calculated coverage zones instantly.
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