Field of view, focal length and camera distance
Three calculations from the same figures: how wide you frame, which focal length to fit, or how much distance you need behind the camera. Sensor sizes from full frame to 1 inch.
The formula, and why it is exact
framed width (m) = sensor width (mm) × distance (m) ÷ focal length (mm)
A lens projects the sensor onto the scene following a plain ratio of triangles. You can check it by hand: a 36 mm sensor, a 36 mm lens, a subject at 5 m — you frame 5 m. The other two calculations are the same equation, solved for the other unknown.
What the calculation does not say, and we have no right to let you believe: the distance is measured from the sensor plane, not from the front of the lens; and the formula ignores distortion and the flange behavior of very short focal lengths. The gap stays negligible beyond about a meter — it stops being negligible in macro.
Sensor widths used
The width actually used in video, which is what decides the field — not the marketing diagonal. Full frame 36 mm · Super 35 24.89 mm · APS-C 23.5 mm · Micro 4/3 17.3 mm · 1 inch 13.2 mm.
Frequently asked
Where is the distance measured from — the lens or the sensor?
From the sensor plane: on a camera body, a small crossed-circle symbol marks it. The gap with the front of the lens is a few centimetres — irrelevant at three meters, noticeable in a close-up. The calculation is an approximation at short distances either way.
Why the sensor width, and not its diagonal?
Because the horizontal field of view depends only on the horizontal dimension. A sensor advertised as “1 inch” does not measure an inch: that is a convention inherited from camera tubes. Its real width is 13.2 mm, and that is what counts.
How exact is the result?
It is a geometric estimate, suited to preparing a shot: framed width ≈ sensor width × distance ÷ focal length. In practice some lenses give a slightly different field, especially at short distances or depending on focus. To pick a focal length or check that a room is big enough, the order of magnitude is plenty.
And if I do not have enough room at home?
That is the most common case, and it is exactly what this calculation makes visible: framing three people head to toe can take several meters of distance, often more than a living room offers. Two ways out: a shorter focal length to widen the field — but if that forces the camera very close to the people, the perspective gets less flattering — or shooting somewhere that has the distance.