On a sunny day (21 Jul 2018 13:11:58 +0100 (BST)) it happened Theo
 wrote in
:

>(you can do without the 'bs' blocksize setting, but the copy will go a lot
>more slowly as it'll copy one byte at a time)

Actually 512 bytes at the time,
and that is often the exact sector size of SDcards,
so normally no need to specify a bigger blocksize.
Try it, makes no difference whatsoever, except for reporting perhaps.
What does make a difference is fast cards, and a fast card reader.

From
man dd
ibs=BYTES
              read up to BYTES bytes at a time (default: 512)
obs=BYTES
              write BYTES bytes at a time (default: 512)

--- SoupGate-Win32 v1.05