Focal Length Equivalent Calculator
When you move a lens between camera bodies with different sensor sizes, the field of view changes even though the focal length of the lens does not. This is because a smaller sensor captures only the central portion of the image the lens projects. A 50mm lens on a full frame body (36x24mm sensor) gives a horizontal angle of view of about 39.6 degrees. The same 50mm lens on an APS-C body (23.5x15.6mm sensor, crop factor 1.5x) gives a horizontal angle of view of about 26.3 degrees, matching what a 75mm lens would give on the full frame body. The equivalent focal length is the focal length you would need on the target sensor to produce the same angle of view as the actual lens on the source sensor. The formula is: equivalent focal length = actual focal length multiplied by (source crop factor divided by target crop factor). This calculator lets you select both the source sensor (where the lens is mounted) and the target sensor (the format you want to compare to), and shows the equivalent focal length and the angle of view on each. It also shows the approximate depth of field difference in stops: at equivalent fields of view, a crop sensor gives roughly the crop factor ratio in stops of additional depth of field compared to full frame when using the same physical aperture.
A 50 mm lens on APS-C Nikon/Sony (1.5x) is equivalent to 75.00 mm on Full frame (1.0x).
How the equivalent focal length is calculated
Each sensor format has a crop factor relative to the full frame 35mm standard (36x24mm diagonal = 43.27mm). The crop factor is 43.27 divided by the sensor diagonal. To find the equivalent focal length between any two formats, multiply the actual focal length by the ratio of the source crop factor to the target crop factor.
Equivalent focal length = actual focal length x (source crop factor / target crop factor)
Angle of view (horizontal) = 2 x arctan(sensor width / (2 x focal length))
Worked example
50mm lens on APS-C Nikon/Sony (crop factor 1.5, sensor width 23.5mm), compared to full frame (crop factor 1.0, sensor width 36mm):
- Equivalent focal length = 50 x (1.5 / 1.0) = 75mm
- Angle of view on APS-C = 2 x arctan(23.5 / 100) = approximately 26.3 degrees
- Angle of view on full frame at 75mm = 2 x arctan(36 / 150) = approximately 26.3 degrees (confirming equivalence)
Both give the same 26.3 degree horizontal angle of view, confirming the equivalence.
Depth of field difference
When comparing cameras at the same field of view, the smaller sensor format requires a shorter physical focal length. A shorter focal length at the same aperture and subject distance produces more depth of field (more of the scene in focus). The approximate difference in stops equals log base 2 of the crop factor ratio between the two sensors. For APS-C (1.5x) vs full frame (1.0x): log2(1.5 / 1.0) = approximately 0.58 stops. The APS-C gives about 0.6 stops more depth of field at equivalent fields of view and the same physical aperture setting. For Micro Four Thirds (2.0x) vs full frame (1.0x): log2(2.0) = 1 stop more depth of field on MFT.
Focal length equivalents: quick reference table
| Full frame focal length | APS-C Canon (1.6x) | APS-C Nikon/Sony (1.5x) | Micro Four Thirds (2.0x) | 1-inch (2.7x) |
|---|---|---|---|---|
| 14mm (ultra wide) | 8.8mm | 9.3mm | 7.0mm | 5.2mm |
| 24mm (wide) | 15.0mm | 16.0mm | 12.0mm | 8.9mm |
| 35mm (standard wide) | 21.9mm | 23.3mm | 17.5mm | 13.0mm |
| 50mm (standard) | 31.3mm | 33.3mm | 25.0mm | 18.5mm |
| 85mm (portrait) | 53.1mm | 56.7mm | 42.5mm | 31.5mm |
| 135mm (short telephoto) | 84.4mm | 90.0mm | 67.5mm | 50.0mm |
| 200mm (telephoto) | 125mm | 133mm | 100mm | 74mm |
| 400mm (super telephoto) | 250mm | 267mm | 200mm | 148mm |
Table shows the lens focal length needed on each crop sensor to produce the same angle of view as the full frame focal length in the first column.
Sensor widths used in calculations
The angle of view calculation uses the physical sensor width for each format. The values used in this calculator are:
| Sensor format | Crop factor | Sensor width (mm) | Sensor height (mm) |
|---|---|---|---|
| Full frame | 1.00 | 36.0 | 24.0 |
| APS-H | 1.26 | 28.7 | 19.0 |
| APS-C Canon | 1.61 | 22.3 | 14.9 |
| APS-C Nikon/Sony | 1.53 | 23.5 | 15.6 |
| Micro Four Thirds | 2.00 | 17.3 | 13.0 |
| 1-inch | 2.73 | 13.2 | 8.8 |
Crop factors are derived from the sensor diagonal relative to the full frame diagonal of 43.27mm. Minor rounding differences exist between sources; the values above are consistent with published manufacturer specifications.
Focal length equivalent calculator: frequently asked questions
What does equivalent focal length mean?
Equivalent focal length is the focal length that would produce the same angle of view on a different sensor format. Because sensors vary in size, a 50mm lens frames a different scene on an APS-C sensor than on a full frame sensor. The equivalent focal length tells you what focal length you would need on the target sensor to get the same framing. It is calculated by multiplying the actual focal length by the ratio of the source sensor crop factor to the target sensor crop factor.
Is a 50mm lens on APS-C the same as 80mm on full frame?
In terms of field of view, yes. A 50mm lens on a Canon APS-C body (1.6x crop factor) produces roughly the same angle of view as an 80mm lens on a full frame body. However, other optical properties differ. The depth of field will be greater on the APS-C body because to match the same field of view you are using a shorter focal length (50mm vs 80mm). At the same aperture and subject distance, a 50mm lens produces more depth of field than an 80mm lens. Background blur (bokeh) will also be more pronounced on the full frame body at equivalent fields of view.
Does a 50mm lens change focal length on a crop sensor?
No. The focal length of a lens is a fixed optical property determined by the lens design and does not change based on the camera body it is mounted on. What changes is the field of view the sensor captures. A smaller sensor captures only the central portion of the image circle the lens projects, which is equivalent to cropping the image. The result looks like a longer focal length, but the lens itself has not changed.
What is the field of view formula?
Horizontal angle of view = 2 x arctan(sensor width / (2 x focal length)). For example, a full frame sensor (36mm wide) with a 50mm lens has a horizontal angle of view of 2 x arctan(36 / 100) = 2 x arctan(0.36) = approximately 39.6 degrees. The same 50mm lens on an APS-C sensor (23.5mm wide) gives 2 x arctan(23.5 / 100) = approximately 26.3 degrees, matching what a 76mm lens would give on full frame.
How do I get a full frame perspective on a crop sensor?
To replicate the angle of view of a given focal length on full frame using a crop sensor, divide the full frame focal length by the crop factor. To replicate a 35mm wide-angle on a full frame body with a 1.5x APS-C body, you need a 35 / 1.5 = 23mm lens. To replicate an 85mm portrait focal length on full frame, you need an 85 / 1.5 = 57mm lens on the APS-C body. Note that depth of field characteristics will still differ between the two setups at the same aperture.
Sources
- Wikipedia: Angle of view.
- Cambridge in Colour: Digital camera sensor sizes.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology. General information only.