Crop Factor Equivalent Calculator

How it is calculated

You enter the lens focal length in millimetres, the sensor's crop factor, and the lens's f-number. The tool multiplies the first and the last by the crop factor: equivalent focal length = focal length × crop factor and equivalent f-number = f-number × crop factor. The first tells you which full-frame lens would give the same angle of view; the second tells you which full-frame aperture would give the same depth of field and background blur at that framing. Focal length is shown to one decimal in millimetres, the aperture as f/ with one decimal, and the crop factor is echoed with two decimals. All three values must be above zero. The lens itself does not change: the f-number still controls exposure, so shutter speed and ISO should be set from the real aperture, not the equivalent one.

Common mistakes

• Entering the focal length already given as 35 mm equivalent on the lens or camera spec. The field expects the real focal length printed on the lens.
• Using the equivalent f-number to set exposure. The lens still passes light at its real f/1.8; the equivalent number only describes depth of field and subject isolation.
• Forgetting the crop factor depends on the sensor, not the lens. A lens on an APS-C body uses about 1.5 (or 1.6 for some brands), and on a Micro Four Thirds body 2.
• Typing the crop factor as a percentage or the sensor size. It is a ratio, such as 1.5, which is the full-frame diagonal divided by the sensor diagonal.
• Applying the factor to a lens already designed for full frame and used on full frame. With a crop factor of 1 the numbers stay unchanged.