CCTV · BS EN 62676-4
CCTV pixel density: how many pixels do you need to identify someone?
How pixel density is worked out, the levels in BS EN 62676-4:2025 from Overview to Scrutinise, a worked example, and why it is only part of the picture.
What pixel density is
Pixel density is the number of pixels a camera puts across each metre of the scene at the target. The standard defines it as the pixels at the target per unit length. In practice you work it out like this:
pixel density = horizontal resolution ÷ width of the scene at the target
The result is in pixels per metre. More pixels per metre means more detail on the person or object you are trying to see.
A worked example
An 8 megapixel camera is 3840 pixels wide. It looks at a scene 20 m wide at the target.
3840 ÷ 20 = 192 pixels per metre.
In the 2025 levels below, 192 is above Perceive (125) and below Characterise (250). The free pixel density calculator does this for you, and shows which level a camera reaches.
The levels in the 2025 edition
BS EN IEC 62676-4:2025 has seven levels, given as minimums in pixels per metre:
| Level | Pixels per metre |
|---|---|
| Overview | 20 |
| Outline | 40 |
| Discern | 80 |
| Perceive | 125 |
| Characterise | 250 |
| Validate | 500 |
| Scrutinise | 1500 |
They replaced the older DORI names of the 2015 edition: Monitor 12.5, Detect 25, Observe 62.5, Recognise 125, Identify 250 and Inspect 1000 pixels per metre. Perceive (125) and Characterise (250) match Recognise and Identify in number.
Working out the width of the scene
The width of the scene at a distance depends on the lens and the size of the sensor:
Scene width = distance × sensor width ÷ focal length
and the angle of view is 2 × atan(sensor width ÷ (2 × focal length)). Many CCTV sensors are wider than they are tall, so use the sensor size from the camera's data sheet. The lens calculator does these sums and draws the view at the real angle.
It is not the whole story
Pixel density does not guarantee a usable picture. It is a simplification. Lighting, the lens, compression, distance and the display all change what you can actually make out. Treat the number as the start of the design, then check the picture.
The 2015 edition is listed by BSI as superseded but still current, replaced by BS EN IEC 62676-4:2025. Check which edition a job or contract works to.
How long to keep the footage
There is no legal minimum or maximum. The ICO and the Surveillance Camera Code of Practice (principle 6) both say to keep footage no longer than you need for your stated purpose, and to write the period in your CCTV policy. The storage calculator works out the disk space for the period you choose.
Common questions
How many pixels per metre do I need to identify someone?
Under the 2015 DORI levels, Identify is 250 pixels per metre and Recognise is 125. In the 2025 edition the matching levels are Characterise (250) and Perceive (125).
How is CCTV pixel density calculated?
Divide the camera's horizontal resolution by the width of the scene at the target, in metres. A camera 3840 pixels wide looking at a scene 20 m wide gives 192 pixels per metre.
What are the DORI levels?
In the 2015 edition: Monitor 12.5, Detect 25, Observe 62.5, Recognise 125, Identify 250 and Inspect 1000 pixels per metre. The 2025 edition uses seven levels, Overview to Scrutinise.
Does a higher pixel density always give a better picture?
No. Pixel density is a simplification. Lighting, the lens, compression, distance and the display also change what you can make out.
This guide is general information for UK fire & security companies, not legal or engineering advice. Always work to the current edition of the relevant standard and your own competent-person judgement.
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