Use the free tool below: your data never leaves your browser — all work happens on your device, and nothing is uploaded to any server.
What crop factor actually changes
Crop factor describes how much smaller a camera sensor is than a full-frame sensor, which measures 36 by 24 millimetres. A smaller sensor records only the middle of the image a lens projects, so the photo looks as if it were taken with a longer lens on a full-frame camera. A 50 mm lens on a camera with a 1.5x crop factor gives the same field of view as a 75 mm lens on full frame. The lens itself does not change. The sensor simply crops the picture, and that crop is where the name comes from.
The calculator above works in both directions. Enter your lens focal length and your sensor, and it returns the full-frame equivalent. Enter a full-frame focal length you want to match, and it returns the lens you need on your sensor. A photographer moving from full frame to Micro Four Thirds, with its 2x crop, learns that a 25 mm lens now frames like the familiar 50 mm, and that a 100 mm equivalent needs only a 50 mm lens. This is the most practical use of the tool: translating focal lengths you already understand into the system you actually own.
The common crop factors, explained
Full frame is the reference at 1.0x. APS-C sensors from Nikon and Sony sit near 1.5x, while Canon APS-C is about 1.6x, a small difference that still matters when you compare lenses. Micro Four Thirds doubles everything at 2.0x. One-inch sensors, common in compact cameras and some drones, sit near 2.7x. Medium format sensors are larger than full frame, so their factor drops below 1.0, around 0.79x, meaning a lens frames wider than it would on full frame. The calculator includes these presets plus a custom option, where it works out the factor from the sensor width you enter.
Two misunderstandings deserve clearing up. First, crop factor does not change exposure. A lens set to f/2.8 gives the same exposure on any sensor, because exposure depends on the aperture and shutter speed, not on the sensor size. Second, crop factor alone does not change depth of field for the same framing. If you step back to frame the same subject with a cropped sensor, the depth of field changes because you moved, not because of the crop itself. Keep these straight and the numbers stay honest.
Choosing lenses with crop factor in mind
Think in equivalents when you shop. If you loved a 35 mm lens on full frame and now shoot APS-C at 1.5x, look for a 24 mm lens, since 24 times 1.5 equals 36, close to your old favourite. If you shoot wildlife on Micro Four Thirds, a 300 mm lens frames like 600 mm on full frame, which is a huge reach advantage in a small, light package. That reach is why many bird photographers like smaller sensors. The price is paid at the wide end: a true wide angle on a cropped sensor needs a very short focal length, and very short lenses cost more and distort more.
Finally, remember that equivalents describe framing only. A 50 mm f/1.8 on a cropped sensor does not become an 75 mm f/1.8 in every sense. The depth of field at the same aperture and framing stays closer to the real lens, and the noise at a given ISO stays closer to the real sensor. Equivalents are a framing shortcut, not a full identity swap between systems, and treating them that way keeps your expectations realistic when you change cameras. The background blur and noise behaviour still belong to the real lens and the real sensor. Use the calculator to plan your framing, then judge blur, low-light performance, and image quality from real photos taken with the combination you are considering. Framing is the easy part. The rest is why trying a lens before buying still matters.
Related calculators
- Spanish version
- Darkroom Enlarger Exposure Calculator – New Print Time When You Raise the Enlarger Head
- Angle of View Calculator – Horizontal, Vertical and Diagonal Coverage of Your Lens