Crop Factor / Equivalent Focal Length Calculator
Enter a lens focal length, its aperture, and the camera's sensor format, and this calculator gives the full-frame equivalent focal length, the depth-of-field equivalent aperture, and the horizontal field of view. Crop factor rescales a lens's angle of view because a smaller sensor records only the centre of the image circle a full-frame body would capture. Use it to compare lenses across formats — a 35 mm on APS-C frames like a 52.5 mm on full-frame.
Equivalent focal length
52.50 mm
35 mm × 1.50 crop factor
Equiv. aperture (DoF)
f/3.00
Horizontal FoV
37.85°
Detail
Actual vs equivalent focal
Compare scenarios
Run the same calculation with two or three input sets side by side. Differences are highlighted; every number comes from the same tested formula as the calculator above.
| Input | Scenario A | Scenario B |
|---|---|---|
| Focal Mm | ||
| Aperture | ||
| Sensor Preset | ||
| Crop Factor | ||
| Sensor Width Mm |
How it works
Equivalent focal length is simply the actual focal length multiplied by the sensor's crop factor. Crop factor is the ratio of the 35 mm full-frame diagonal to the sensor's diagonal: 1.0 for full-frame, 1.5 for most APS-C bodies (Nikon, Sony, Fuji, Pentax), 1.6 for Canon APS-C, and 2.0 for Micro Four Thirds. A 35 mm lens on a 1.5× sensor frames the same scene as a 52.5 mm lens would on full-frame, so choose a preset or type a custom crop factor for any other format.
Equivalent aperture multiplies the actual f-number by the same crop factor (f/2 on a 1.5× sensor behaves like f/3.0). This is the depth-of-field and total-light equivalence convention: it tells you the full-frame f-number that would produce the same background blur and gather the same total light across the frame. It is deliberately not an exposure equivalence — for metering and shutter speed the lens keeps its marked f-number.
Horizontal field of view is computed from the sensor width and the actual focal length as 2 × arctan(sensor width ÷ (2 × focal length)), converted to degrees. Because it uses the real sensor width rather than the crop factor alone, the angle you see reflects the specific sensor: the same lens shows a wider view on a broader sensor and a narrower view on a smaller one. This is the geometric angle of view and ignores lens distortion.
Frequently asked questions
What is crop factor, and does it change the lens itself?+
No. Crop factor is a comparison tool, not a physical change to the lens. A 35 mm lens is always a 35 mm lens with the same optics and the same amount of background blur it always had. What changes is how much of the projected image the sensor records: a smaller sensor captures a tighter central crop, so the framing matches a longer lens on full-frame. The 'equivalent focal length' answers one question only — what full-frame focal length would frame the same scene — and does not mean the lens has become that lens.
Why is the equivalent aperture different from the f-number on the lens?+
Because it answers a different question. The equivalent aperture (aperture × crop factor) describes depth of field and total light gathered, not exposure. An f/2 lens on a 1.5× sensor gives roughly the same background blur and collects the same total light as an f/3.0 lens on full-frame — useful when comparing how 'fast' a system is for subject isolation. But for exposure the lens still meters at f/2: your shutter speed and ISO are set by the marked f-number, not the equivalent one. This calculator reports the equivalent purely for cross-format DoF and light comparison.
Why does the field of view depend on the sensor and not just the crop factor?+
Field of view is a geometric relationship between the physical sensor dimensions and the focal length, so two sensors with the same nominal crop factor but slightly different widths will give slightly different angles. This tool computes the horizontal angle from the sensor width and focal length directly, which is more precise than scaling a single full-frame FoV by the crop factor. It reports the horizontal angle; vertical and diagonal angles differ because they use the sensor's height and diagonal instead. The result is the ideal geometric angle and does not account for lens distortion, vignetting, or in-camera cropping modes.