I am trying to determine the proper stripe value for an EXT4 mounted on a MD RAID5. I have 4 physical drives in the array, my chunk size is 64k and FS is using 4kB blocks.

man page says:
Number of filesystem blocks that mballoc will try to use for allocation size and alignment. For RAID5/6 systems this should be the number of data disks * RAID chunk size in filesystem blocks.

If I let mount read the value from the SB it uses 4096.

If I do the math I get:
3 * 64 * 4 = 768

What is the correct formula for calculating the stripe size?

When I do that same math I get 3 * 64k / 4k = 48 FS blocks.

Yes, 48 makes sense, as that is the defined stripe width when I created the array.

Ext4 allows you to specify a "stripe=" mount option. I am confused as to what this value should be. As stated before if I do not specify the "stripe=" option to mount the default (presumably from the SB) is 4096. Nowhere is it specified that stripe == stripe width.