By Ahsan Khowaja · Updated 27 October 2026
How to use the field of view calculator
- Choose what you want to work out. The default is a camera: sensor size plus focal length gives the angle the picture covers.
- Pick your sensor size. If yours isn't listed, choose Custom and type the width and height in millimetres from the camera's spec sheet.
- Type the focal length printed on the lens (the real one, such as 4.3 mm on a compact, not the "24 mm equivalent" from the box).
- Add a distance if you want to know how much of the scene fits in the frame at that range.
You get three angles. Horizontal is across the long side of the picture, vertical across the short side and diagonal corner to corner. Lens makers usually quote the diagonal figure, while CCTV and machine-vision makers tend to quote the horizontal one, so check which you are comparing.
The other modes cover the rest of what people mean by FOV: the lens needed for a given angle, the width an angle covers at a distance (binoculars and scopes), converting a game's FOV between screen shapes, the angle a monitor fills from your seat (sim racing), and a telescope eyepiece's true field.
The field of view formula
For a lens focused at a distance, the angle of view across one side of the sensor is:
Angle = 2 × atan(d ÷ 2f)
- d is the sensor dimension in millimetres: its width for the horizontal angle, its height for the vertical one, or its diagonal (√(width² + height²)) for the diagonal angle.
- f is the focal length in millimetres.
- atan is the inverse tangent, in degrees.
The scene covered at a distance follows from similar triangles: scene width = distance × sensor width ÷ focal length. The same applies to the height.
Worked examples, the same ones the calculator is tested against:
- Full frame, 50 mm: 2 × atan(36 ÷ 100) = 39.6° across, 27.0° vertical and 46.8° diagonal. At 10 m the frame covers 10 × 36 ÷ 50 = 7.2 m by 4.8 m.
- Full frame, 24 mm: 2 × atan(36 ÷ 48) = 73.7° across and 84.1° diagonal, a typical wide-angle view.
- 1/3-inch CCTV camera, 2.8 mm lens: the sensor is about 4.8 × 3.6 mm, so 2 × atan(4.8 ÷ 5.6) = 81.2° across. At 10 m it sees a strip 17.14 m wide.
These figures assume a normal (rectilinear) lens focused far away. Fisheye lenses follow a different projection, and focusing close usually narrows the view a little.
Camera field of view chart (full frame)
Horizontal, vertical and diagonal angles for common focal lengths on a 36 × 24 mm sensor, plus the width covered at 10 m:
| Focal length | Horizontal | Vertical | Diagonal | Width at 10 m |
|---|---|---|---|---|
| 14 mm | 104.3° | 81.2° | 114.2° | 25.71 m |
| 20 mm | 84.0° | 61.9° | 94.5° | 18.00 m |
| 24 mm | 73.7° | 53.1° | 84.1° | 15.00 m |
| 35 mm | 54.4° | 37.8° | 63.4° | 10.29 m |
| 50 mm | 39.6° | 27.0° | 46.8° | 7.20 m |
| 85 mm | 23.9° | 16.1° | 28.6° | 4.24 m |
| 135 mm | 15.2° | 10.2° | 18.2° | 2.67 m |
| 200 mm | 10.3° | 6.9° | 12.3° | 1.80 m |
| 400 mm | 5.2° | 3.4° | 6.2° | 0.90 m |
On a smaller sensor the same lens sees less. A 50 mm lens on an APS-C body of about 23.5 mm width covers 26.4° across, much like a 75 mm lens on full frame. The crop factor calculator does that conversion for any sensor.
Field of view to focal length
To go the other way, from an angle you want to a lens, rearrange the formula: f = d ÷ (2 × tan(angle ÷ 2)). For 90° across a full-frame sensor, f = 36 ÷ (2 × tan 45°) = 18 mm. That lens also gives 67.4° vertically and 100.5° diagonally. For 60° across an APS-C sensor of about 23.5 mm, f = 23.5 ÷ 1.1547 = 20.35 mm.
Choose "Focal length for a wanted field of view" and say whether your angle is horizontal, vertical or diagonal. If you know the size of the subject and its distance rather than an angle, the focal length calculator works it out from those directly.
Security camera field of view calculator
CCTV lenses are short and the sensors small, so the sensor size matters as much as the lens. A 2.8 mm lens is wide on a 1/3-inch sensor (81.2°) but would be far wider on a bigger chip. Use the camera mode with the sensor type from the camera's data sheet, and enter the distance to the area you want covered. The "scene covered" row tells you whether a driveway or a shop counter fits.
The "1/3-inch" in a sensor name doesn't measure anything on the chip. These names come from old video camera tubes, and the light-sensitive area is far smaller than the name suggests: a 1/3-inch type is only about 6 mm across the diagonal. That is why the presets list approximate sizes in millimetres, and why the maker's data sheet is the best source for your exact camera.
Binocular field of view calculator
Binoculars and rifle scopes state their field either as an angle (such as 8°) or as a width at a set range, like "420 ft at 1,000 yards" or "140 m at 1,000 m". The "width covered by an angle" mode converts between them: for 8°, 2 × 1,000 m × tan 4° = 139.85 m at 1,000 m, and about 420 ft at 1,000 yards. The same mode works for any field of view converter job: enter any angle and any distance to see how wide an area it spans.
Telescope field of view calculator
For visual astronomy, choose the telescope mode. Magnification is the telescope's focal length divided by the eyepiece's focal length, and the true field is roughly the eyepiece's apparent field divided by that magnification. A 1,200 mm telescope with a 25 mm eyepiece magnifies 48×. With a 50° eyepiece the true field is 50 ÷ 48 = 1.04°, enough to fit about two full Moons side by side, since the Moon is about half a degree across. The apparent field is printed on the eyepiece or in its specs. For an exact figure, divide the eyepiece's field stop diameter by the telescope's focal length and multiply by 57.3.
As a FOV calculator for astrophotography, use the camera mode with the telescope's focal length as the lens. A full-frame camera on a 1,200 mm scope covers 2 × atan(36 ÷ 2,400) = 1.72° (103 arcminutes) across, which tells you whether a nebula or galaxy will fit in one frame.
Game FOV: horizontal to vertical FOV
Games describe the same view in different ways. Some set the horizontal angle, others the vertical one, and some quote a horizontal FOV measured against a 4:3 screen. The vertical angle stays the same on every screen shape, so convert through it:
Horizontal = 2 × atan(tan(vertical ÷ 2) × width ÷ height)
- 90° horizontal on 16:9 is 58.7° vertical.
- 90° horizontal on 4:3 becomes 106.3° horizontal on a 16:9 screen with the same vertical view. That is why a "90" setting can look wider than 90° on a widescreen monitor.
- 70° vertical on 16:9 is 102.4° horizontal.
The 21:9 preset is exactly 2.33:1. A 3440 × 1440 monitor is about 2.39:1, so for that one choose Custom and type 3440 and 1440.
Screen field of view for sim racing
For driving and flight games, the realistic setting is the angle your screen really fills from where you sit. When the game's FOV matches it, speeds, distances and corners look the right size. Enter the screen's diagonal, its aspect ratio and the distance from your eyes:
- A 27-inch 16:9 monitor is about 59.8 × 33.6 cm. At 60 cm from your eyes it fills 53.0° across and 31.3° vertically.
- Three of those screens, with the side screens turned in by 53.0° so each one faces you, fill 158.9°. Bezels are ignored.
- A 55-inch TV at 2 m fills only 33.9° across, which is why racing on a TV across the room needs a narrow in-game FOV to look true to scale.
The TV viewing distance calculator and the screen size calculator help if you are still choosing a screen.
