Crop factor,
explained — with a tool that shows it
▸ See it in the simulator
Crop factor is the single most misunderstood number in cameras — and the easiest to see once someone shows you. In one line: a smaller sensor captures a narrower slice of what your lens projects, so the image looks more zoomed-in. Crop factor is just how much smaller that sensor is than full frame.
43.27mm is the diagonal of a full-frame (36×24mm) sensor. Divide it by your sensor's diagonal and you get the crop factor. To find what a lens "becomes," multiply:
So a 25mm lens on a 2× Micro Four Thirds sensor frames like a 50mm on full frame. The lens didn't change — the sensor is just seeing less of its image.
| Format | Sensor size | Crop factor | A 50mm becomes |
|---|---|---|---|
| Medium format | 43.8 × 32.9 mm | 0.79× | ~40mm |
| Full frame | 36 × 24 mm | 1.0× | 50mm |
| Super 35 | ~24.6 × 13.8 mm | ~1.5× | ~75mm |
| APS-C | ~23.5 × 15.6 mm | ~1.5× | ~75mm |
| Micro Four Thirds | 17.3 × 13 mm | 2.0× | 100mm |
| Super 16 | ~12.5 × 7 mm | ~3.0× | ~150mm |
Browse the exact crop factor of any body in the camera database — every figure is derived from the real sensor dimensions.
Numbers are abstract; framing isn't. The focalcomp simulator draws the exact field of view of any camera-and-lens combination on one fixed scene, so you can watch crop factor tighten the frame.
Partly — a speed booster optically widens a full-frame lens back toward its native field of view on a smaller sensor (and adds a stop of light). It's the closest thing to cancelling crop factor, which is why they're so popular on Micro Four Thirds and Super 35 bodies.
Read the speed-booster guide →Does crop factor change the actual focal length?
No. A 50mm lens is always 50mm. Crop factor only describes how much of that lens's image the smaller sensor captures — it changes field of view, not optics, depth of field's focal component, or the glass itself.
Is a crop sensor bad?
Not at all — it just frames tighter, which is an advantage for reach (wildlife, sports) and a disadvantage for wide shots. Super 35, the cinema standard for a century, is a "crop" sensor.
How do I know my camera's crop factor?
Look it up on its focalcomp page — or divide 43.27 by your sensor's diagonal. Most spec sheets list the sensor dimensions.