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Focal Length for Framing Calculator (Distance, Subject Size & Field of View)

Work out which focal length frames a subject of a given size from a given distance on your sensor — or how far back to stand with the lens you have, or how wide a scene a lens covers at a distance — with horizontal, vertical and diagonal angles of view, the full-frame equivalent and a table of common focal lengths.

Solve for

Subject / scene width to fill the frame

Distance to the subject

Focal length (for distance/coverage modes)

Sensor

Orientation

Breathing room around the subject

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How it works

scene width = sensor width × (distance − f) ÷ f · f = sensor width × distance ÷ (scene width + sensor width) · angle of view = 2 × atan(sensor dimension ÷ 2f) · full-frame equivalent = f × 43.3 ÷ sensor diagonal

A lens forms an image in which the ratio of image size to subject size equals the ratio of focal length to subject distance — the similar triangles of the thin-lens model — so for a given sensor the scene width that fills the frame is proportional to distance and inversely proportional to focal length. Turn that around and you can pick a lens for a shot before you get there: the space available and the size of the subject fix the focal length, and a percentage of breathing room keeps heads off the edge. Because the same angle of view on a smaller sensor needs a shorter focal length, the crop factor converts between formats, but the perspective — how big the background looks relative to the subject — depends only on where you stand.

Worked example

To fit a 1.8 m person with 10% room from 5 m on a full-frame camera in landscape you need 36 × 5,000 ÷ (1,980 + 36) ≈ 89 mm — an 85 mm is the lens, covering 2.08 × 1.39 m with a 23.9° horizontal angle of view. On APS-C the same shot wants about 58 mm (a 50 mm from 4.3 m); turning the camera to portrait, about 60 mm on full frame frames the standing figure.

Frequently asked questions

Does this account for focus breathing?

No — many lenses shorten their effective focal length when focused close (some 70–200 mm zooms act like 135 mm at 1.5 m). At portrait distances expect the real framing to be a little wider than calculated.

How do I frame a group?

Allow about 0.6 m of width per standing person and 20% margin; for 8 people (5 m) at 6 m on full frame that is about 36 mm — or 24 mm on APS-C.

Related calculators

Field of View Angle Calculator

Work out the horizontal, vertical and diagonal angle of view for any lens and sensor — and how wide a scene it covers at a given distance.

Crop Factor Equivalent Focal Length Calculator

See what focal length your lens really behaves like on a crop sensor — plus the equivalent aperture for depth of field.

Bokeh & Background Blur Calculator

Work out how blurred the background will be: blur disc size on the sensor, as a percentage of the frame and in pixels, from focal length, aperture, subject distance or framing, background distance and sensor size. Includes depth of field on the subject, a blur-versus-distance chart and a same-framing lens comparison (50 mm f/1.4 vs 85 mm f/1.8 vs 135 mm f/2 vs a phone).

Depth of Field Calculator

Find the near limit, far limit and total depth of field for any lens, aperture and focus distance — plus the hyperfocal distance for your sensor.

Standard optics and digital-audio arithmetic with idealised assumptions (thin lens, circular aperture, uncompressed PCM). Real lenses, codecs and rooms differ; use it for planning and comparison.