How is full-frame equivalent focal length calculated?

Multiply the native focal length by the format's crop factor. A 35 mm lens on a 1.5× APS-C body has a full-frame equivalent of 35 × 1.5 = 52.5 mm, meaning it frames the scene like a 52.5 mm lens would on full-frame. The crop factor is the ratio of sensor diagonals.

Does a crop sensor change the actual focal length of a lens?

No. A 50 mm lens is always 50 mm regardless of the body it is mounted on. The smaller sensor simply records a tighter crop of the projected image, which narrows the field of view, so the equivalent focal length describes framing, not the lens's physical optics.

What crop factors do common formats use?

Full-frame is 1.0×, Nikon, Sony, and Fuji APS-C are about 1.5×, Canon APS-C is roughly 1.6×, Micro Four Thirds is 2.0×, the 1-inch type is about 2.7×, and the popular 44×33 medium format is about 0.79×. This tool uses these standard values to build the comparison.

Why does field of view matter more than focal length?

Field of view is what you actually see in the frame, and it depends on both focal length and sensor size. Comparing the angle of view lets you match framing across systems precisely, which is why the table shows the horizontal angle for each format alongside the focal length.

Does equivalence affect depth of field and exposure too?

Equivalent focal length matches framing but not everything. A smaller sensor at the same equivalent framing and aperture gives more depth of field and gathers less total light, so an f/2.8 on Micro Four Thirds behaves like roughly f/5.6 full-frame for background blur, even though exposure brightness is unchanged.

Focal Length Equivalence Table

Switching camera systems means re-learning your focal lengths, because the same lens frames differently on each sensor size. This tool shows the full-frame equivalent of any lens and the native focal length you would need on every other format to keep the same framing.

How it works

The full-frame equivalent normalises the field of view across formats:

equivalent focal length = native focal length × crop factor

The crop factor is the ratio of the full-frame sensor diagonal to the format’s diagonal — 1.5× for most APS-C, 2.0× for Micro Four Thirds, 0.79× for 44×33 medium format. To find the native focal length on another format that matches the same framing:

native (other format) = equivalent ÷ crop factor of that format

The table also reports the horizontal angle of view, computed from the focal length and sensor width:

angle of view = 2 × arctan(sensor width ÷ (2 × focal length))

Worked example

A 50 mm lens on full-frame has a crop factor of 1.0, so its equivalent is 50 mm with roughly a 40° horizontal angle of view. To match that framing:

APS-C (1.5×): 50 ÷ 1.5 ≈ 33 mm native
Micro Four Thirds (2.0×): 50 ÷ 2.0 = 25 mm native
Medium format (0.79×): 50 ÷ 0.79 ≈ 63 mm native

All four lenses give the same field of view despite very different focal lengths.

Tips and notes

The number engraved on a lens never changes — only the sensor’s crop of the image circle does.
Equivalent focal length matches framing only; depth of field and total light gathered still differ between formats.
A smaller sensor at the same equivalent framing and aperture renders more depth of field, so background blur shrinks even when exposure stays the same.
All maths runs locally in your browser; nothing about your gear is uploaded.