What pixel density (PPM) means for CCTV resolution
Pixel density, or pixels per metre (PPM), is the number of horizontal pixels a camera lands on each metre of scene width: PPM = horizontal pixels ÷ scene width in metres. It is the metric that decides what an operator can actually do with the footage — far more than the megapixel headline alone, because the same camera spread across a wider scene resolves fewer pixels per metre. Pixels per foot is the density divided by 3.281.
DORI tiers (IEC 62676-4 minimum horizontal pixel densities)
The DORI scale is defined by IEC 62676-4 — Video surveillance systems for use in security applications — Part 4: Application guidelines. Each tier is a minimum horizontal pixel density needed for an operator task:
- Detect — 25 px/m: Tell that a person or object is present in the scene.
- Observe — 62.5 px/m: Follow movement and note characteristic details such as distinctive clothing.
- Recognise — 125 px/m: Say with confidence whether a person shown is the same as one seen before.
- Identify — 250 px/m: Establish the identity of an individual beyond reasonable doubt.
- Inspect — 1000 px/m: Read fine forensic detail — a vehicle number plate or banknote serial within the field of view.
Camera resolution presets (nominal horizontal pixels)
The calculator carries the following nominal horizontal pixel formats. These are sensor-format pixel budgets across the scene; real usable detail is reduced by lens quality, scene contrast, lighting, motion blur and codec compression.
- 1MP / 720p: 1280 horizontal pixels (nominal).
- 2MP / 1080p: 1920 horizontal pixels (nominal).
- 4MP: 2560 horizontal pixels (nominal).
- 5MP: 2944 horizontal pixels (nominal).
- 6MP: 3072 horizontal pixels (nominal).
- 8MP / 4K: 3840 horizontal pixels (nominal).
- 12MP: 4000 horizontal pixels (nominal).
Frequently asked questions
- What resolution do I need to identify a person?
- Identification under IEC 62676-4 needs at least 250 pixels per metre of scene width. The maximum scene width that still identifies for a given camera is its nominal horizontal pixels divided by 250 — so an 8MP / 4K camera (3840 px) identifies across roughly 15.4 metres, and a 2MP / 1080p camera (1920 px) across roughly 7.7 metres.
- What is the difference between recognise and identify?
- Recognise (125 px/m) lets an operator say whether a person is the same as someone seen before; identify (250 px/m) is the higher, evidential standard of establishing identity beyond reasonable doubt. Recognise covers twice the scene width of identify for the same camera.
- Is megapixel count enough on its own?
- No. A high-megapixel camera spread across a wide scene can still fall below Recognise. Pixel density depends on both the resolution and the scene width the camera has to cover, which is why this calculator works from PPM rather than megapixels alone.
CCTV Resolution / PPM Calculator — DORI pixel density (IEC 62676-4)
— Calculator · CCTV resolution & pixel density (DORI)
Scene width, resolution — pixels per metre.
Set the horizontal scene width you need to cover and a camera resolution. The calculator returns the pixel density (px/m and px/ft), the DORI tier achieved and the maximum scene width that still meets each tier. IEC 62676-4 criteria, cited.
Pixel density
427
px/m · 130 px/ft
DORI tier achieved
Identify
≥ 250 px/m
Scene width
6.00
m · 4MP
4MP identifies a face up to ~10.2 m wide; recognises up to ~20.5 m. Resolution pixels are nominal sensor formats — real usable detail is reduced by lens, scene, lighting and compression. This is a planning sense-check, not a survey or a camera layout.
A planning link — not a quote.
- resolution
- 4MP · 2560 px wide (nominal)
- scene width
- 6.00 m
- density
- 427 px/m · 130 px/ft
- achieved
- Identify (Establish the identity of an individual beyond reasonable doubt.)
Max scene width per tier — 4MP
| Tier | Min px/m | Max width |
|---|---|---|
| Detect | 25 | 102 m(336 ft) |
| Observe | 62.5 | 41.0 m(134 ft) |
| Recognise | 125 | 20.5 m(67 ft) |
| Identify | 250 | 10.2 m(34 ft) |
| Inspect | 1000 | 2.56 m(8 ft) |
Max width = nominal horizontal pixels ÷ the tier's minimum px/m. Wider scenes than this fall below the tier.
What changes this estimate
- Lens quality, focus & optical resolving power
- Scene contrast, lighting & motion blur
- Codec compression at the recorded bitrate
- Where the subject sits within the field of view
Source
IEC 62676-4 — DORI pixel-density criteria (Detect / Observe / Recognise / Identify)IEC 62676-4 · retrieved 2026-06-27
A planning link — not a quote.
Quick answer
Pixel density (PPM) is horizontal pixels divided by scene width in metres — the metric that decides whether footage can detect, observe, recognise or identify a person. This calculator returns the PPM, the DORI tier achieved against the IEC 62676-4 criteria, and the maximum scene width that still meets each tier for a chosen resolution. It is a planning sense-check on the optics, not a survey or a camera layout.
When to use
Early scoping of what camera resolution a scene needs to reach Recognise or Identify, before a surveillance design — and to sanity-check a megapixel claim against the scene width it has to cover.
When not to use
It does not place cameras, produce a security or camera layout, or replace a site survey — resolution pixels are nominal, and real usable detail depends on the lens, lighting, scene contrast and compression.
· Why it matters
Megapixel marketing answers the wrong question. A 12MP camera covering a 40-metre forecourt resolves only ~100 px/m — below Recognise — while a humble 2MP camera on a 1.5-metre doorway clears Identify with room to spare. What matters is pixels per metre across the scene, measured against the IEC 62676-4 DORI tiers: Detect 25, Observe 62.5, Recognise 125, Identify 250, Inspect 1000 px/m. This calculator turns a scene width and a resolution into the tier you actually achieve, and the widest scene each tier survives — so the resolution conversation starts from the task, not the spec sheet.
· Frequently asked
CCTV resolution / PPM —
what people ask first.
How is pixel density (PPM) calculated?
PPM = horizontal pixels ÷ scene width in metres. A 4MP camera (2560 horizontal pixels) covering a 6 m scene gives 2560 ÷ 6 ≈ 427 px/m — comfortably above the Identify threshold of 250 px/m. Pixels per foot is the same figure divided by 3.281.
What are the DORI pixel-density tiers?
IEC 62676-4 defines minimum horizontal pixel densities for four operator tasks: Detect (25 px/m — someone is present), Observe (62.5 px/m — follow movement and note details), Recognise (125 px/m — is this the same person as before), Identify (250 px/m — establish identity beyond reasonable doubt). Inspect (1000 px/m) is the forensic tier used above Identify for reading fine detail such as a number plate within the field of view.
What is the maximum scene width I can identify across?
For a given camera it is the nominal horizontal pixels divided by 250 (the Identify threshold). An 8MP / 4K camera (3840 px) identifies across roughly 15.4 m; a 2MP / 1080p camera (1920 px) across roughly 7.7 m. Recognise covers twice that width, because its threshold is half.
Why does the calculator say resolution pixels are nominal?
Because the megapixel format is the theoretical pixel budget, not the usable detail. Lens resolving power, focus, scene contrast, low light, motion blur and codec compression all reduce how much of that nominal density survives to the recorded frame. The PPM figure is a planning sense-check, not a guarantee of resolved detail — a site test confirms the real result.
Does this replace a CCTV survey or camera layout?
No. It sizes the optics question — what resolution a scene needs to reach a DORI tier — at an early planning stage. It does not place cameras, design coverage, specify a security layout, or recommend a product. Those follow from a survey and a technical design conversation.
· Begin
Planning a surveillance scene
properly?
Send the scenes that matter — the entrances, the tills, the perimeter — and the identity standard each one needs to meet. We respond within two working days with a resolution and lens note for each view, as the start of a surveillance design conversation.