CCTV lens calculator: field of view, scene width and DORI distances
Work out what area a camera covers with a given lens, how many pixels fall on each metre at the distance you need, and how far the detail is enough to detect, recognize and identify a person. Everything is calculated in your browser and drawn to scale right away, and you can share a link to the result with an engineer.
Camera
Optional: without it the angle is derived from the frame aspect ratio
Used only to suggest a focal length in the “From the task” mode
Scene
Along the camera axis — to the plane perpendicular to it
Result
Estimate- Horizontal angle
- 90°
- Vertical angle
- 58.7°
- Diagonal angle
- 97.9°
- Scene width
- 20 m
- Scene height
- 11.2 m
- Horizontal density
- 128 px/m
The vertical angle is derived from the horizontal one and the frame proportions — check it against the datasheet.
The drawing is to the same scale as the calculation
Turn on height and tilt to see the side view with the blind zone under the camera.
Levels of detail · IEC 62676-4:2014
| Level | Threshold | At 10 m | Range along the axis |
|---|---|---|---|
Detect you can say with confidence that a person is in the frame | 25 px/m | ✓ yes | ≤ 51.2 m |
Observe actions and details are visible: clothing, items in hand | 62.5 px/m | ✓ yes | ≤ 20.5 m |
Recognize a known person can be recognised | 125 px/m | ✓ yes | ≤ 10.2 m |
Identify an unknown person can be identified | 250 px/m | no | ≤ 5.12 m |
The pixel density of the selected level is reached on paper, under idealised geometry. Whether the image is fit for purpose is confirmed by on-site testing: light, video compression, object speed and the operator’s screen all affect the result.
We will select cameras for your site
Send the calculation to an engineer: they will pick in-stock models with datasheet angles, suggest mounting points and price the system.
How to use it
- 1Choose a mode. “From camera specs” shows what a particular camera delivers. “From the task” answers the reverse question: what angle, focal length and resolution you need to see an area of a given width with the required detail.
- 2Enter the horizontal field of view and the resolution from the camera datasheet. The angle is stated for each lens separately: the same model with a 2.8 mm and a 4 mm lens has different angles. If you know the sensor dimensions in millimetres, switch to “Sensor and focal length”.
- 3Set the distance. Without height it is the distance along the camera axis. With height and tilt it is the distance along the ground from the point below the camera to the object, and the calculator converts it into depth along the axis.
- 4Compare the result with the level table: the marked rows are reached at the set distance, and the range column shows how far each level holds. You can copy the calculation or send it to an engineer with a request.
How it is calculated
The calculator uses the rectilinear (pinhole) lens model — the same model camera manufacturers and system designers use. Notation: Sw and Sh are the width and height of the active sensor area, f is the focal length, D is the depth along the camera axis, Nx is the number of horizontal pixels, H and h are the camera and target heights, τ is the tilt.
When the datasheet angle is known, the calculation starts from it rather than from the sensor size: the datasheet angle already accounts for cropping and the specifics of the lens. Depth along the axis and distance along the ground are different quantities. For a camera 4 m up looking at a face 10 m from the pole, the depth is more than 10 m, so the density on the face is slightly lower than a ground-distance calculation would suggest.
A 4 MP camera (2560 × 1440 pixels) with a 90° angle sees a scene 20 m wide at 10 m and delivers 128 px/m — the DORI recognition level. To identify a person in a 3 m wide passage from the same spot, 750 pixels across are enough, but the angle has to be narrowed to 17.1° — with a varifocal lens, for example.
Levels of detail under IEC 62676-4
Pixel density is the number of frame pixels per metre of scene width at the object’s position. It is the key figure when choosing a lens: megapixels alone do not tell you whether a face 15 metres away will be distinguishable.
The international standard IEC 62676-4 links density to surveillance tasks. The 2014 edition introduced six levels, four of which are used in most projects — DORI: detect (25 px/m), observe (62.5), recognize (125) and identify (250).
The second edition came out in October 2025. It completely revised the scale: there are now seven levels from 20 to 1,500 px/m in two groups — low density for perimeters and open areas and high density for work with people and vehicles. Levels of the two editions are not equated with each other even where the thresholds match, so the calculator keeps them in separate profiles.
The thresholds are a design guideline. They describe an image assessed by a person on a screen and do not carry over directly to video analytics, automatic plate recognition or thermal cameras, which have their own requirements. The calculation is not a certificate of compliance with the standard.
| Level | Threshold | What it gives |
|---|---|---|
| Monitor | 12.5 px/m | you can see whether people are in the area and where they are heading |
| Detect | 25 px/m | you can say with confidence that a person is in the frame |
| Observe | 62.5 px/m | actions and details are visible: clothing, items in hand |
| Recognize | 125 px/m | a known person can be recognised |
| Identify | 250 px/m | an unknown person can be identified |
| Inspect | 1000 px/m | fine details are visible: lettering, banknotes, small objects |
| Level | Threshold | What it gives |
|---|---|---|
| Overview | 20 px/m | general situation, a distant moving object is noticeable |
| Outline | 40 px/m | object shapes are distinguishable and movement can be tracked |
| Discern | 80 px/m | a person can be told apart from a vehicle or an animal |
| Perceive | 125 px/m | presence and movement are clear, object features are not yet distinguishable |
| Characterize | 250 px/m | object features are visible: a person’s gait, a vehicle type |
| Validate | 500 px/m | a known person can be verified, a licence plate can be read |
| Scrutinize | 1500 px/m | detail comparable to a passport photo |
Assumptions and limits
- The model is rectilinear: it does not apply to fisheye, panoramic or multi-sensor cameras.
- Density is calculated horizontally at the object’s position; towards the edges of the frame real lenses lose detail because of distortion.
- Digital zoom enlarges the picture but does not add pixels on the object, so it does not increase detail.
- Lighting, IR illumination, shutter speed and object speed, video compression and bitrate, and sensor noise at night all affect the result.
- Viewing angle matters for identification: a face filmed from above at a steep angle is harder to make out than a frontal one at the same density.
- An operator sees the detail only if the screen shows the frame at sufficient resolution: an 8 MP camera in a 4 × 4 grid on a Full HD monitor loses most of its detail.
- Trees, poles, and glare from headlights and the sun are not part of the calculation — they are checked on site.