How is the subject distance calculated?

Using the thin-lens magnification relation. The required field-of-view height is the subject height divided by the fraction of the frame it should fill. Distance equals focal length times field height divided by sensor height. Longer lenses need more distance for the same framing.

What is the angle of view?

It is the angular extent of the scene the lens captures, measured at the sensor. It is computed as two times the arctangent of half the sensor dimension divided by the focal length. The diagonal angle is what manufacturers usually quote.

Why does sensor size matter?

A smaller sensor crops into the image circle, so the same focal length captures a narrower angle of view and frames the subject more tightly. That is why a 50mm lens behaves like a short telephoto on APS-C but as a standard lens on full frame.

What frame fill percentage should I use for portraits?

A head-and-shoulders portrait fills roughly 60 to 80 percent of the frame height. A full-length portrait fills around 90 percent leaving headroom and floor. A tight beauty crop can exceed 100 percent of the visible head. Adjust the slider to match your composition.

Does this account for focus breathing or close-focus magnification?

It uses the ideal thin-lens model, which is accurate for normal shooting distances. At extreme close range, real lenses deviate because the effective focal length and the principal-plane position shift. For macro work, use a dedicated magnification calculator.

What is the Subject Distance & Angle of View Calculator?

Compute the camera-to-subject distance required to fill a chosen percentage of the frame with a subject of known size, for any focal length and sensor format. Also returns the horizontal, vertical and diagonal angle of view. It runs free in your browser on Gera Tools, with nothing uploaded.

Subject Distance & Angle of View Calculator

Name: Subject Distance & Angle of View Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Knowing exactly where to stand turns guesswork into a setup. This calculator works out the camera-to-subject distance you need to frame a subject of known size at a chosen tightness, for any lens and sensor — and tells you the angle of view and total field captured at that point.

How it works

The calculation rests on the thin-lens magnification relation. To frame a subject of height S so that it fills a fraction f of the frame, the field of view at the subject must be:

field height (FOV) = S ÷ f

The lens projects that field onto the sensor of height h, and for a subject at distance D with focal length F the geometry gives:

D = F × (FOV ÷ h)

So for a 1.7 m subject filling 90% of the frame height on a full-frame sensor (h = 24 mm) with an 85 mm lens:

FOV = 1.7 ÷ 0.90 = 1.889 m = 1889 mm
D = 85 × (1889 ÷ 24) ≈ 6.69 m

Angle of view

The angle of view is independent of the subject and depends only on the lens and sensor:

angle = 2 × arctan( sensor dimension ÷ (2 × focal length) )

Computed separately for sensor width, height and diagonal. The diagonal figure is the one lens makers print on the box.

Notes and tips

Crop sensors frame tighter. The same 50mm on APS-C needs you to step back further than on full frame to keep the same composition.
Watch perspective, not just framing. Standing further back with a longer lens compresses features — flattering for portraits; standing close with a wide lens exaggerates them.
Real distances are slightly longer than the thin-lens figure at close range because the lens has physical length, but the model is accurate for typical portrait and product distances.

All calculations run locally in your browser.