Sensor Crop Factor Calculator
Crop factor tells you how a lens behaves on a sensor smaller than full frame. It is the ratio of the full-frame 35mm diagonal (about 43.27 mm) to your sensor's diagonal. Enter your sensor's width and height in millimeters and a lens focal length, and this calculator returns the crop factor, the sensor diagonal, and the 35mm equivalent focal length. The reference diagonal is a fixed geometric value, so the result is exact math rather than an estimate. Use it to compare lenses across camera systems on equal footing.
Crop factor formula
Full-frame diagonal = sqrt(36^2 + 24^2) = 43.2666 mm
Sensor diagonal = sqrt(width^2 + height^2)
Crop factor = 43.2666 / sensor diagonal
Equivalent focal = focal length * crop factor
Sensor area = width * height
The 43.2666 mm reference is the diagonal of the 36 by 24 mm full-frame format. A smaller sensor has a shorter diagonal and therefore a crop factor above 1, which multiplies the apparent focal length.
Common sensor sizes
- Full frame: 36 by 24 mm, crop factor 1.0 by definition.
- APS-C: around 23.6 by 15.7 mm, crop factor near 1.5 (about 1.6 for some makers).
- Micro Four Thirds: 17.3 by 13 mm, crop factor about 2.0.
- One-inch type: around 13.2 by 8.8 mm, crop factor about 2.7.
- Enter your camera's exact sensor dimensions for a precise factor.
Crop factor: frequently asked questions
What is sensor crop factor?
Crop factor is the ratio of a full-frame 35mm sensor's diagonal to your sensor's diagonal. Full frame measures 36 by 24 mm, a diagonal of about 43.27 mm. A smaller sensor has a larger crop factor, meaning a given lens frames a narrower view than it would on full frame.
How is crop factor calculated?
Crop factor equals 43.27 divided by the square root of your sensor width squared plus height squared. For an APS-C sensor of 23.6 by 15.7 mm, the diagonal is about 28.4 mm, giving a crop factor of roughly 1.52.
What is equivalent focal length?
Equivalent focal length is your lens focal length times the crop factor, expressing the field of view as the full-frame focal length that would match it. A 50 mm lens on a 1.5x crop sensor frames like a 75 mm lens on full frame.
Where does 43.27 mm come from?
It is the diagonal of the 36 by 24 mm full-frame 35mm format, computed as the square root of 36 squared plus 24 squared. This is the reference diagonal against which all crop factors are measured, a fixed geometric value.
Does crop factor change my lens aperture?
It does not change the f-number that controls exposure, but the equivalent depth of field and the equivalent aperture for that field of view scale with the crop factor too. This calculator focuses on field of view via equivalent focal length.
Official sources
- National Institute of Standards and Technology: millimeter unit reference.
- International Organization for Standardization: ISO 1009 photographic 35mm format.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.