📐 Security Camera Field of View Calculator

Enter your camera's field-of-view angle (from its spec sheet) and the distance to what you're monitoring, to see how wide an area it covers.

Distance to subject (ft)

Camera field of view (degrees)

How the coverage width is worked out

The lens angle and the distance form an isosceles triangle, split down the middle into two right triangles:

coverage width = 2 × distance × tan(FOV / 2)

2 × 20 × tan(55°) = 57.1 ft

Width scales linearly with distance, so the same 110° camera covers 28.6 ft at 10 ft and 114.3 ft at 40 ft. What it does not tell you is whether anything in that width is recognisable, which is the question that actually matters.

Coverage is not the same as usable detail

Spread a fixed sensor over a wider scene and each foot gets fewer pixels. For a 1080p camera, 1920 pixels across, at 20 ft:

Lens FOV	Width at 20 ft	Pixels per foot
60°	23.1 ft	83
90°	40.0 ft	48
110°	57.1 ft	34
130°	85.8 ft	22

The usual rule of thumb is about 40 pixels per foot to identify an unfamiliar face, 20 to recognise someone you know, and 10 to register that a person is there. A wide lens buys area at the cost of that detail, and adds barrel distortion at the frame edges.

Published FOV is a manufacturer figure measured under ideal conditions, and it is usually the diagonal angle, which is wider than the horizontal one this triangle implies - so the real horizontal width is often narrower than the answer. Night-time IR range is quoted separately, in total darkness against a reflective target. Entering 180° or more breaks the tangent and returns a meaningless or negative width.

Frequently asked questions

How wide an area does a 110 degree camera cover?

57.1 ft across at 20 ft away, and 28.6 ft at 10 ft. The width doubles whenever the distance doubles.

Is the field of view on a spec sheet horizontal or diagonal?

Almost always diagonal, since it is the larger number. If the camera lists all three, enter the horizontal angle - a diagonal figure overstates the width across the scene.

How many pixels per foot do I need to identify a face?

Around 40 as a working figure, which a 1080p camera reaches only over about 48 ft of scene width. Halve the coverage or double the resolution to get there; lighting and motion blur can still undo it.