Lens2Lens is a Lens Equivalence Calculator.

Lens2Lens trys and replicate the look of a lens (the DoF and FoV) from one sensor (camera 1), to a different sized sensor (camera 2) by suggesting an equivalent lens and t-stop to use.

Lens2lens calculates an equivalent lens by using a comparison of the sensor sizes of the two cameras, plus the lens focal length and apature on camera 1.

The lens focal length, and apature that lens2lens suggests for camera 2 is the closest match to the the DoF (specifically hyper focal length), and FoV seen on camera 1.

To find an equivalent lens enter the focal length and current appature of the lens on camera 1, and select the Sensor sizes for cameras 1 and 2.

Lens2Lens has four presets with different sensor size settings (in mm):
35mm (22 x 12.375), RED 2K (11.06 x 6.22), RED 3K (16.59 x 9.33), and RED 4K (22.12 x 12.44)

You can change the Aspect ratio of the sensor on camera 1 and 2 by going to “More Settings”, and selecting the desired aspect for each camera.
Apect ratio only affects presets, not custom sensor sizes.

You can create your own custom sensor size for camera 1 and 2 by going to “More Settings”, turning on the “Custom Sensor Size” switch for the appropriate camera and entering the W x H (in mm).

Similarly if your lenses were designed for another sensor size than the camera you are using them on (i.e Nikon lenses on a RED) you can add a custom Lens Magnification Factor (LMF) in “More Settings” too.
A Nikon lens LMF on RED is around 1.52.