Field of View Calculator
Calculate the horizontal coverage width (and height) at a given subject distance for any lens, sensor, and crop factor combination. Perfect for planning surveillance setups, portrait framing, or landscape compositions.
About this calculator
Field of view (FOV) is the real-world area visible through a lens at a given distance. The horizontal coverage width is: FOV_width = 2 × distance × tan(arctan(sensorWidth / (2 × focalLength × cropFactor))). Here, sensorWidth / (2 × focalLength × cropFactor) is the half-angle tangent of the lens on the effective (cropped) focal length. Multiplying by 2 × distance converts that half-angle into a full width at the subject plane. The crop factor accounts for sensors smaller than the full-frame 35 mm standard — a crop factor of 1.5 on an APS-C body makes a 50 mm lens behave like a 75 mm lens in terms of field of view. Vertical FOV is computed identically using sensorHeight in place of sensorWidth. This formula assumes a rectilinear (non-fisheye) lens and a flat subject plane perpendicular to the optical axis.
How to use
You have a 50 mm lens on a full-frame camera (sensorWidth = 36 mm, cropFactor = 1) shooting a group portrait at 3 m distance. FOV_width = 2 × 3 × tan(arctan(36 / (2 × 50 × 1))) = 6 × tan(arctan(0.36)) = 6 × 0.36 = 2.16 m. So your frame captures roughly 2.16 m of width at 3 m — enough for about 5–6 people standing shoulder to shoulder. If you switch to an APS-C body (cropFactor = 1.5), the same lens gives FOV_width = 6 × tan(arctan(36 / (2 × 50 × 1.5))) = 6 × tan(arctan(0.24)) ≈ 6 × 0.235 = 1.41 m, noticeably tighter.
Frequently asked questions
How does focal length affect the field of view of a camera lens?
Shorter focal lengths produce a wider field of view, while longer focal lengths narrow it. This is because a shorter focal length bends light more sharply, capturing a larger angle of the scene onto the same sensor. For instance, a 24 mm wide-angle lens might capture 74° horizontally on a full-frame sensor, while a 200 mm telephoto lens captures just about 10°. Changing focal length is the primary way photographers control how much of a scene fits in the frame from a fixed position.
What is crop factor and how does it change the effective field of view?
Crop factor describes how much smaller a camera's sensor is compared with a 35 mm full-frame sensor (36 × 24 mm). A common APS-C sensor has a crop factor of 1.5–1.6×, meaning the sensor captures only the central portion of the image circle a lens projects. This effectively multiplies the lens's focal length equivalently — a 35 mm lens on a 1.5× crop body behaves like a 52.5 mm lens on full frame in terms of field of view. For telephoto reach this is beneficial, but it can be limiting for wide-angle work.
How do I calculate how wide an area my security camera covers at a given distance?
Use the field of view formula: coverage width = 2 × distance × tan(arctan(sensorWidth / (2 × focalLength × cropFactor))). You need the camera's sensor width (often 1/3" or 1/2.7" chips with ~4–6 mm width), the lens focal length (typically 2.8–8 mm for security cameras), and the monitoring distance. For example, a 2.8 mm lens on a 1/3" sensor (sensorWidth ≈ 4.8 mm, cropFactor ≈ 1) at 5 m gives coverage of about 2 × 5 × tan(arctan(4.8/5.6)) ≈ 8.6 m wide. This helps you determine how many cameras are needed to cover a given area without blind spots.