Focal Length Calculator
Work out a lens’s angle of view and its full-frame-equivalent focal length based on your camera’s sensor crop factor.
What This Calculator Does
This tool converts a lens’s actual focal length into its full-frame (35mm) equivalent, and estimates the horizontal angle of view your sensor and lens combination will capture. It’s useful for comparing lenses across cameras with different sensor sizes, such as APS-C, Micro Four Thirds, or medium format bodies.
The Formula
The 35mm equivalent focal length is calculated as actual focal length × crop factor. The crop factor compares your sensor’s diagonal to a full-frame sensor’s diagonal — common values are about 1.5x for APS-C, 1.6x for Canon APS-C, and 2.0x for Micro Four Thirds. The horizontal angle of view uses the formula 2 × arctan(sensor width / (2 × focal length)), which describes the field captured based on sensor width and true focal length.
A Few Notes
- Crop factor and sensor width vary by camera model — check your manufacturer’s specs for exact figures.
- This estimate assumes a rectilinear lens; fisheye and other specialty lenses behave differently.
- Intended for general photography planning and educational purposes.