Help with resizing large Sony A7R4 files

Hi all.
I need to export TIFFs at two different sizes. 50MB 8bit and 100MB 16bit.
I’m currently scanning with the Sony A7R4 which yields roughly 120MB RAW files.
This is what I’m converting from.
Any help on how to reach my two target file sizes when I’m exporting from lightroom?

If your version is like my Lightroom 6.14 Perpetual then the image size options are in terms of pixel dimensions, which I’ve always thought was the most meaningful way to go anyway.

So, short answer, try ‘Long edge = 5121 pixels’ and your down-sized image should be 5121 x 3414 pixels. You’ll need to state the resolution as well which normally is taken to be 300 ppi but it makes no difference to the file size, and of course either an 8-bit or 16-bit Tiff format. I’m assuming that your image is still at the standard 3:2 aspect ratio. The resulting 8-bit tiff might be slightly larger on disc than 50MB but you will have recorded 50MB of data so it should open in Photoshop as a 50MB uncompressed file, the 16-bit version will be twice the size. Presumably no problem rounding it up to ‘Long edge = 5200 pixels’ if you prefer, to give a 51.6 MB 8-bit file once opened in Photoshop.

Note that the slightly awkward maths is because 1MB = 1024 x 1024 bytes, so 10488576 bytes. Some sites suggest that 1MB is 1 million bytes but Photoshop wouldn’t agree with them.

Fortunately 1 Megapixel (MP) is 1 million pixels so the calculation for the number of megapixels of the final image (or your camera sensor) is much easier but in terms of data storage you are storing 3 channels - Red, Green & Blue.

The latest version of Lightroom Classic has the ability to set the export file size in the Export menu item. In the File Settings area, you can set the file type and size. You can also use the method above and set the pixel/measurement options in the Image Size dialogue box.