Camera Field of View Cones, Explained

A camera dot on a floor plan tells you a camera exists. It tells you nothing about what the camera sees. Two cameras in the same spot with different lenses cover completely different parts of a room, and on a plan they look identical.

A field-of-view cone fixes that. It is a wedge drawn from the camera, and it encodes two things:

• The angle: how wide the camera sees, in degrees. This is a property of the lens and the sensor, not something you choose freely.
• The range: how far out the wedge extends before the image stops being useful for what you need it for. This one is widely misunderstood, and it is covered further down.

Point the cone in the direction the camera faces and you have a coverage map. Do it for every camera and the blind spots appear on their own, without anyone having to imagine them.

You will also hear this called a cone of vision, a view cone, a coverage cone or a cone of sight. Same thing.

Cameras are sold by focal length in millimetres. Coverage is drawn in degrees. The conversion is the piece most people have to look up every time, so here it is.

These are horizontal angles for a 1/2.8 inch sensor, which is the common size for fixed IP cameras. A larger sensor at the same focal length sees wider, so treat these as a working approximation and check the spec sheet when the shot is tight.

Lens	Horizontal field of view	Typically used for
2.8mm	~100–110°	Small rooms, entries, corridors end to end
3.6mm	~85–90°	General purpose, most retail floors
4mm	~80–85°	General purpose, slightly more reach
6mm	~50–55°	Long aisles, parking rows, driveways
8mm	~40°	Distant gates, loading docks
12mm	~25–30°	Licence plates, long approaches

Two shortcuts worth remembering. Wider lens, wider cone, shorter useful range. And a 360 or fisheye camera is not a wide cone at all, it is a full circle, which is why it belongs in the middle of a space rather than on a wall.

This is the part that separates a coverage drawing that survives a walkthrough from one that does not.

"How far can the camera see" is the wrong question. A camera can see a person at 200 feet. Whether you can tell who they are at 200 feet is a completely different matter, and it is the one that decides whether the footage is any use when something happens.

The industry has a standard for this, DORI, from IEC 62676-4. It defines four levels by how many pixels land across each metre of the scene:

Level	Pixels per metre	What you can actually do
Detection	25 px/m	Tell that a person is there
Observation	62.5 px/m	See what they are doing, characteristic clothing
Recognition	125 px/m	Tell it is somebody you already know
Identification	250 px/m	Identify a stranger from the footage alone

Pixel density falls off with distance, so one camera hits all four levels at different ranges. The same camera might identify at 15 feet, recognise at 30, and only detect at 90.

So the cone length should be drawn to the level the job requires. A camera watching a cash drawer needs identification distance. A camera watching a back fence needs detection. Drawing both cones out to "as far as it can see" makes the plan look like full coverage and hides the fact that half of it is unusable for the purpose it was bought for.

If a customer ever asks why they cannot make out a face on footage from a camera that clearly "covers" the area, this table is the answer.

Once every camera on the plan has a cone, four things become obvious that were invisible before:

• Blind spots. The white space between wedges. On a dotted plan you argue about these on site; on a coned plan you see them in the office.
• Wasteful overlap. Two cameras covering the same aisle from similar angles is a camera you did not need to sell, or worse, one you did sell and cannot justify.
• Cameras aimed at nothing. A wedge pointing into a wall three feet away is a mounting position that needs rethinking, and it is very easy to miss when the camera is just a dot.
• Whether the lens choice was right. If your 2.8mm cone only reaches a third of the way down a long aisle at recognition distance, the drawing tells you before the install does.

The practical value is that it moves the argument earlier. A coverage gap found on a drawing costs a conversation. The same gap found after the cable is in the ceiling costs a truck roll and an awkward call.

Historically this meant CAD, or a coverage tool separate from wherever the rest of the design lived, which is why a lot of proposals go out with camera dots and no cones at all.

It does not have to be that. In FieldMarkup every camera icon carries a cone: drag to aim it, adjust the angle to match the lens, set the range to the distance the job actually needs. It sits on the same floor plan as the device schedule and the bill of materials, so the coverage drawing and the parts list are the same document rather than two things to keep in sync.

If you want the click-by-click version, that is in the FOV cones guide in the learning centre. If you would rather just try it, the demo opens the editor with a sample plan and no signup.