Effective Focal Length Calculator
Convert lens focal length to 35mm equivalent (effective focal length) using crop factor. Useful for APS-C, Micro Four Thirds, and other crop sensors. Formula: EFL = focal length × crop factor.
Use Calculator ↓Effective Focal Length Formula
EFL = f × crop factor
f = lens focal length (mm), crop factor = sensor size relative to full frame (35mm).
What is Effective Focal Length?
Effective focal length (EFL) is the focal length in 35mm (full-frame) equivalent. Crop sensors capture a smaller area, so the same lens gives a narrower field of view; multiplying by the crop factor gives the equivalent focal length on full frame.
To compute the physical focal length of a single lens from curvature and refractive index, use our focal length calculator. For the combined focal length of two lenses, see the lens combination calculator.