What this calculator does
A lens produces the same physical focal length regardless of which camera it is mounted on, but a smaller sensor only captures the centre portion of that image circle, which narrows the field of view. Crop factor equivalent focal length restates that narrower field of view as the focal length a full-frame camera would need to match it.
This is why a 50mm lens looks noticeably more telephoto on a cropped-sensor camera than on a full-frame one: the lens itself has not changed, but the smaller sensor is only using the middle of the frame, which has the same visual effect as using a longer lens on a full-frame body.
The formula
Multiply the lens focal length by the sensor’s crop factor to get the full-frame-equivalent focal length. The crop factor is set by how much smaller the sensor is than a full-frame sensor: commonly around 1.5 for APS-C, 1.6 for some APS-C systems, and 2.0 for Micro Four Thirds.
| Term | Meaning |
|---|---|
| Crop factor | How much smaller a sensor is than full frame, expressed as a multiplier on the diagonal. |
| Equivalent focal length | The full-frame focal length that would produce the same field of view: focal length × crop factor. |
| Field of view | How wide or narrow a scene the lens captures, which is what crop factor actually changes. |
The inputs explained
| Field | What to enter |
|---|---|
| Lens focal length (mm) (mm) | The actual, physical focal length printed on the lens, in millimetres. |
| Sensor crop factor | The crop factor of the camera’s sensor relative to full frame, such as 1.5 or 1.6 for APS-C, or 2.0 for Micro Four Thirds. |
When to use it
Choosing a lens for a cropped-sensor body
Working out the equivalent focal length before buying a lens shows what field of view it will actually deliver on that specific camera, rather than assuming it behaves as it would on full frame.
Comparing gear across formats
A photographer moving between a full-frame and a cropped-sensor system can use the equivalent focal length to pick a matching lens for a similar look on either body.
Explaining apparent reach for telephoto work
Wildlife and sports photographers often favour cropped sensors specifically because the same physical lens reaches further in equivalent focal length terms, without the size and cost of a longer lens.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How equivalent focal length changes with crop factor at a fixed lens
A fixed 50mm lens, across a range of sensor crop factors.
How equivalent focal length changes with the physical lens at a fixed crop factor
A fixed 1.5× crop factor, across a range of physical lens focal lengths.
| Lens focal length | Full-frame equivalent focal length |
|---|---|
| 24 mm | 36.0 mm |
| 35 mm | 52.5 mm |
| 50 mm | 75.0 mm |
| 85 mm | 127.5 mm |
| 100 mm | 150.0 mm |
| 200 mm | 300.0 mm |
Questions
Does crop factor change the aperture too?
The f-stop marked on the lens does not change, since it is a ratio of focal length to aperture diameter, not affected by sensor size. Depth of field and low-light gathering, however, are affected by sensor size in practice, which is a separate discussion from the field-of-view calculation here.
Is this the same as digital zoom?
No. Digital zoom crops and upscales an image after capture, throwing away resolution. A smaller sensor capturing a narrower field of view still uses its full native resolution across that smaller frame, so no image quality is lost the way it is with digital zoom.
What crop factor does my camera have?
It depends on the specific sensor format: common values are around 1.5 for most APS-C cameras, 1.6 for some APS-C systems, and 2.0 for Micro Four Thirds. Check the camera manufacturer’s specifications for the exact figure.
How is this different from aspect ratio?
Aspect ratio describes the width-to-height shape of the frame, such as 3:2 or 4:3, and does not by itself change the field of view captured at a given focal length. Crop factor describes how much of the lens’s image circle a sensor captures, which is what actually narrows or widens the field of view.
To see how that same lens and aperture combination affects sharpness range on a given sensor, use the depth of field calculator.