Full Frame Equivalent
Also called effective focal length: the number you'd need on full frame to match what a lens actually frames on its own sensor. The lens's real, physical focal length never changes — only this comparison figure does.
It's field-of-view-specific and says nothing about exposure or depth of field — a lens's real f-number governs exposure regardless of sensor size, and a separate depth-of-field-equivalent aperture calculation exists for that comparison instead. See the effective focal length answer page for a worked example.
Frequently Asked Questions
Why do smartphone camera specs always list full-frame-equivalent focal lengths?
Because a smartphone's real focal length is often a tiny, unfamiliar number given its small sensor, so manufacturers convert to the full-frame-equivalent figure for a reference most photographers already understand intuitively.
Is full-frame equivalent the same as 35mm equivalent?
Yes — the two terms are interchangeable, since full-frame digital sensors were deliberately built to match 35mm still film's exact dimensions from the outset.
Does full-frame equivalent apply to aperture too, not just focal length?
Focal length and aperture get separate equivalent calculations — a full-frame-equivalent focal length describes field of view, while an equivalent aperture describes depth of field, and the two numbers are rarely identical for the same lens and sensor combination.