About this tool
Crop Factor & Equivalent Focal Length Calculator is a free, in-browser tool that translates a lens between sensor formats. Choose your sensor (or enter its diagonal), a lens focal length and an aperture, and it returns the crop factor, the 35mm-equivalent focal length that gives the same field of view, and the aperture that matches the depth of field on full frame. Everything runs locally with nothing uploaded.
The crop factor is 43.27 / sensor diagonal in millimetres, where 43.27 mm is the full-frame diagonal. The 35mm-equivalent focal length is focal × crop factor, so a 50 mm lens on a 1.6× Canon APS-C body frames like an ≈80 mm lens on full frame. The depth-of-field-equivalent aperture is f-number × crop factor, which is why a smaller sensor gives more apparent depth of field at the same nominal f-stop.
Use it when comparing lenses across cameras, choosing a focal length that reproduces a look you know from another body, or understanding why the same f/2.8 lens renders backgrounds differently on APS-C, Micro 4/3 or a 1-inch sensor.