Zend certified PHP/Magento developer

How to output disk size in GB only with no rounding error?

Output disk size in GB only. Giga Bytes only.
Not MB. Not Mega Bytes.
Not TB. Not Tera Bytes.

Tested thus far:

sudo blockdev --getsize64 /dev/sda
1000204886016

sudo blockdev --getsize64 /dev/sda |bc -l |awk '{print $1/1000000000}'
1000.2

sudo blockdev --getsize64 /dev/sda |bc -l |awk '{print $1/1000000000}' |numfmt --field=1- --format=%.0f --invalid=ignore
1001

But above 1001 output is a rounding error.
1000 is ideal output, meaning 1000 GB disk size.

Question1:
How to fix above rounding error?

Question2:
What is a more elegant way or shorter way versus 120 characters below:
sudo blockdev --getsize64 /dev/sda |bc -l |awk '{print $1/1000000000}' |numfmt --field=1- --format=%.0f --invalid=ignore

.
.

using:
neofetch --stdout |grep 'OS:'

OS: Kubuntu 22.04.3 LTS x86_64