Calculate crop factor

Compare sensor diagonal with full frame and calculate framing-equivalent focal length.

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ToolCrop Factor Calculator
Input
Output
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Preview

How it works

Crop factor is full-frame diagonal divided by selected sensor diagonal. Equivalent focal length multiplies physical focal length by that factor for framing comparison.

  • Full-frame 36×24 mm is the reference.
  • Crop factor describes framing rather than exposure.

Worked example

50mm on APS-C Canon
Crop factor 1.61, so a 50mm behaves like an 80.5mm
Input
											Focal length mm: 50
Aperture: 1.8
Output
												Crop factor: 1.61
Equivalent focal length mm: 80.66
Equivalent aperture: 2.9
Sensor diagonal mm: 26.82

When to use this

Photographers compare lenses, reviews explain equivalent framing, and buyers compare sensor formats.

Edge cases

  • Equivalent focal length changes comparison, not the lens’s physical focal length.
  • Crop factor does not multiply shutter or ISO for equal exposure.
  • Different aspect ratios can make diagonal comparison differ from horizontal framing.