Crop Factor Calculator

Crop factor describes how a camera sensor's diagonal compares with the diagonal of the familiar 36 by 24 millimeter full-frame format. A smaller sensor captures a narrower portion of the image circle projected by a lens, so photographers often describe its view using an equivalent full-frame focal length. This calculator accepts any active sensor width and height, making it useful for APS-C, Micro Four Thirds, one-inch, medium-format, cinema, and custom sensor formats. The calculator first finds the sensor diagonal with the Pythagorean theorem. It then divides the full-frame diagonal, approximately 43.27 millimeters, by the entered diagonal. A 28.34 millimeter APS-C diagonal therefore produces a crop factor near 1.53. Multiplying the lens's actual focal length by this factor gives the 35mm equivalent focal length. A 35 millimeter lens on that sensor frames approximately like a 53.4 millimeter lens on full frame when cameras use the same aspect ratio and shooting position. Crop factor does not physically change focal length, aperture, magnification, or the optical properties printed on a lens. It is a field-of-view comparison. The calculator also reports horizontal field of view from sensor width and actual focal length. That angle is often more directly useful for planning interiors, landscapes, surveillance coverage, and camera placement. Equivalent focal length remains convenient for communicating the expected composition to photographers familiar with full frame. Use the actual imaging area rather than a marketing format name when precision matters. Two cameras both called APS-C can have slightly different dimensions and therefore different factors. Video modes may crop the sensor further, stabilization can trim the recorded area, and anamorphic lenses require additional treatment. The field-of-view formula also assumes a rectilinear lens focused near infinity; distortion and focus breathing can alter real framing. Depth of field comparisons require more context. From the same position with the same actual lens and aperture, cropping does not change the optical depth of field, although enlarging the smaller capture changes the final appearance. Matching composition across formats usually requires changing focal length or camera distance, which does affect depth of field. Treat crop factor as a practical framing conversion, then consider aperture, subject distance, resolution, and output size separately when comparing complete camera systems.