35mm Equivalent Focal Length and Crop Factor Calculator
Convert an actual focal length to the 35mm equivalent focal length from the sensor size or the crop factor, or work back from a 35mm equivalent to the actual focal length.
The 35mm equivalent focal length and the crop factor
The 35mm equivalent focal length is the focal length that gives the same angle of view (the diagonal angle of view) on a 35mm-format (full-frame) camera as the lens gives on a camera with a smaller sensor. The actual focal length of the lens does not change when it is used on a smaller sensor; only the part of the image it covers changes.
- Crop factor = diagonal of the full frame ÷ diagonal of the sensor
- 35mm equivalent focal length = actual focal length × crop factor
What "35mm" refers to
"35mm" refers to the 35mm film format, whose frame is 36 × 24 mm. Its diagonal is √(36² + 24²) = √1,872 ≈ 43.27 mm. This calculator uses that frame as the reference. Wikipedia's article on the crop factor defines the crop factor as the ratio of the diagonal of a 35 mm frame (it gives 43.3 mm) to the diagonal of the sensor, and says that multiplying a lens's focal length by the crop factor gives the focal length that would produce the same field of view on the reference format (checked October 31, 2026). The 36 × 24 mm size is widely used as the frame of the 35mm format, and this calculator uses it as the reference. It is not a value quoted from the text of a standard.
Sensor size presets and where they come from
| Preset | Size (mm) | Crop factor (calculated) | Source |
|---|---|---|---|
| Full frame (35mm format) | 36 × 24 | 1 | Canon, "Image sensor sizes" (about 36 × 24 mm) |
| APS-H | 27.9 × 18.6 | about 1.290 | Canon, "Image sensor sizes" (varies by camera model) |
| APS-C (Canon) | 22.3 × 14.9 | about 1.613 | Canon, "Image sensor sizes" (varies by camera model) |
| APS-C (Nikon DX) | 23.5 × 15.6 | about 1.534 | Nikon D3500 and D5300 specification tables (23.5 × 15.6 mm CMOS sensor, Nikon DX format) |
- The sources are Canon's Japanese-language page "Image sensor sizes", Nikon's Japanese-language page "Basics of the FX and DX formats" and the D3500 specifications (checked October 26, 2026 for the Japanese version of this calculator; not opened again for this page).
- Sizes differ a little between camera models (even APS-C differs between manufacturers and models). For a more exact conversion, enter the size from your camera's specification table.
- For sizes that are not listed, such as Micro Four Thirds, 1-inch type and medium format, enter the size yourself.
Calculated values and manufacturers' stated values differ a little
The crop factor calculated from the sensor size is about 1.613 for APS-C (Canon, 22.3 × 14.9) and about 1.534 for APS-C (Nikon, 23.5 × 15.6). The "about 1.6x" and "about 1.5x" that manufacturers use are rounded common names and differ a little from the calculated values (Nikon describes the DX format as about 1.5 times the FX format). To convert with a stated value, choose "Convert from the crop factor".
Examples
- A 50mm lens on full frame: crop factor 1, equivalent 50mm
- A 50mm lens on APS-C (Canon, 22.3 × 14.9): factor about 1.613, equivalent about 80.66mm
- A 50mm lens on APS-C (Nikon, 23.5 × 15.6): factor about 1.534, equivalent about 76.7mm
- A 50mm lens with a stated factor of 1.5x: equivalent 75mm
- Reverse: to get the angle of view of a 35mm equivalent of 85mm on a camera with a factor of 1.5, the actual focal length is about 56.67mm
Notes
- This converts the angle of view (diagonal) only. The aperture (f-number), depth of field and the amount of background blur are not converted.
- For sensors with a different aspect ratio (such as 4:3 and 3:2), the horizontal and vertical angles of view are not the same even when the diagonal angle is.
- Lens distortion and the change in effective focal length at close range are not included.
- The diagonal is approximated with an integer square root to 40 decimal places (the exact value when the diagonal is a perfect square). Results are shown with 7 significant digits, and a value that includes an approximation is labeled "rounded value".
- The focal length, the sensor dimensions and the crop factor must be numbers greater than 0, with up to 9 digits before the decimal point and 6 decimal places.
Frequently asked questions
What does "35mm equivalent 24mm" mean?
It means the same angle of view as a 24mm lens on a 35mm-format (full-frame) camera. On a camera with a smaller sensor, the actual focal length is 24 ÷ the crop factor.
What happens when the crop factor is larger?
The smaller the sensor, the larger the crop factor, and the same lens gives a narrower angle of view (a more telephoto look).
Is the crop factor of a medium format camera below 1?
A sensor larger than full frame has a crop factor below 1 (the same lens gives a wider angle of view). Enter the sensor size yourself to convert.