Crop factors for common sensor sizes:
Full Frame: 1
APS-C: 1.5
APS-C (Canon): 1.6
APS-H: 1.3
Medium Format (Digital): 0.79
Medium Format: 0.64
How to use the crop factors:
To find the full frame equivalent focal length and maximum aperture of a lens, multiple by the crop factor.
Examples:
Nikon AF-S DX 16-80mm f/2.8-4E ED VR is equivalent to 24mm-120mm ~f/4-5.6
Fujifilm 110mm f/2 is equivalent to ~85mm f/1.5