If you can use Python and pip, you can solve this with humanize. (Thanks to Pyrocater for the idea.)
$ pip install humanize
$ bytes=35672345337
$ python -c "import humanize; print(humanize.naturalsize($bytes))"
35.7 GB
$ seq 0 750000 2250000 |python -c $'import sys, humanize\nfor n in sys.stdin: print(humanize.naturalsize(n))'
0 Bytes
750.0 kB
1.5 MB
2.2 MB