Convert a lens's actual focal length to its full-frame equivalent using your camera's crop factor.
Calculator verified • Last updated: August 2026
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This is the field of view a full-frame camera would need this focal length to match — the lens's actual optical focal length and aperture don't change.
A sensor smaller than full frame captures a narrower crop of the image a lens projects, which narrows the field of view exactly as if a longer lens had been used on a full-frame sensor. The crop factor is the ratio between the two sensor diagonals, and multiplying it by the lens's actual focal length gives the full-frame-equivalent focal length — the number photographers typically use to compare field of view across different camera systems.
$$f_{eff} = f_{actual} \times C$$
f_{actual}: the lens's true, physical focal length, in millimeters.
C: the sensor's crop factor relative to full frame.
f_{eff}: the full-frame-equivalent focal length, in millimeters.
A 50mm lens mounted on a Canon APS-C body (crop factor 1.6x): the effective focal length is 50 times 1.6, or 80mm. That 50mm lens frames a shot on this camera the way an 80mm lens would frame it on a full-frame body — noticeably more zoomed in, even though the lens itself is still physically a 50mm lens.
Assuming crop factor changes the lens's actual aperture is a common misunderstanding — a 50mm f/1.8 lens is still an f/1.8 lens for exposure purposes on any sensor size; only the framed field of view changes, not the amount of light the aperture physically admits.
Applying the crop factor twice (once to the focal length and again separately when comparing depth of field or exposure) double-counts the effect — the crop factor by itself only converts field of view, and should be applied once for that specific comparison.
Crop Factor — the ratio between a full-frame sensor's diagonal and a smaller sensor's diagonal, describing how much narrower that sensor's field of view is at the same focal length.
Full-Frame-Equivalent Focal Length — the focal length a full-frame sensor would need to match a given lens's field of view on a smaller sensor.
APS-C — a common smaller sensor size used in many consumer and enthusiast cameras, with a crop factor around 1.5x-1.6x depending on the manufacturer.
Crop factor is the ratio between a full-frame sensor's diagonal and a smaller sensor's diagonal. It describes how much narrower a smaller sensor's field of view is compared to full frame at the same focal length.
A smaller sensor captures a narrower crop out of the same lens's projected image circle, so it only sees the center portion — the same field of view a longer lens would produce on a full-frame sensor. The lens's actual focal length and optical properties (like its widest aperture) don't change, only the captured field of view does.
The lens's true aperture (f-number) and light-gathering ability don't change with crop factor — only the field of view does. Depth of field is affected indirectly, since a smaller sensor requires more enlargement to reach the same output size, which is a separate effect from the field-of-view crop.