What it's for
The crop factor compares a sensor's size to the full-frame (35mm) sensor, photography's historical reference. This calculator gives you the crop factor of the chosen format and converts the focal length (and, if given, the aperture) to its full-frame equivalent — useful for comparing lenses across different systems.
Formulas used
Crop factor: factor = 43.27 / sensor_diagonal, where 43.27mm is the approximate diagonal of a full-frame sensor (36×24mm), and the chosen sensor's diagonal is found via Pythagoras from its width and height. Equivalent focal length: equivalent_focal = focal_length × crop_factor. If aperture is given, we also show equivalent_aperture = aperture × crop_factor, purely as a reference for full-frame-comparable depth of field/light gathering — the lens's real aperture (and exposure) doesn't change.
Crop factors by format
Full Frame: 1.0x (reference); APS-C Canon: about 1.6x; APS-C Nikon/Sony: about 1.5x; Micro 4/3: 2.0x; 1-inch: about 2.7x; smartphone sensors: vary widely, but typically fall between 5x and 8x depending on the model.
Worked example
A 50mm lens on an APS-C Nikon/Sony camera (1.5x factor) frames equivalently to a 75mm lens on a full-frame camera.
Why "equivalent aperture" is just a comparison
The aperture equivalence is meant to compare how much background blur (depth of field) and relative light two systems capture to produce an image with the same framing and visual exposure — it doesn't change the actual exposure value recorded by the camera, which is still set by the lens's physical aperture.
Frequently asked questions
Does the crop factor change the photo's exposure?
No. The equivalent aperture is only a depth-of-field and relative light-gathering comparison between sensor formats — actual exposure is still set by the physical aperture, ISO and shutter speed of the camera used.
Why is full frame the reference (1.0x)?
Because the full-frame format (36×24mm) matches traditional 35mm film, historically photography's standard — so every other format is usually compared against it.
Is the crop factor the same across all smartphones?
No — it varies a lot between models and even between the different lenses on the same phone (wide, telephoto, etc.), since each one can use a differently sized sensor.