Filament volume and length

PLA

Density: 1.25 g/cm^3
Volume: 0.80 cm^3/g or 800 cm^3/kg
1.75 mm filament length for 1 kg spool: ~ 330 meters / ~ 1080 feet
3.00 mm filament length for 1 kg spool: ~ 110 meters / ~ 360 feet

ABS

Density: 1.04 g/cm^3
Volume: 0.96 cm^3/g or 960 cm^3/kg
1.75 mm filament length for 1 kg spool: ~ 400 meters / ~ 1310 feet
3.00 mm filament length for 1 kg spool: ~ 130 meters / ~ 430 feet

Is it safe to delete the hidden folder $Windows.~WS and $Windows.~BT?

They are both temporary directories used by windows to update your system.
It is safe to delete both to reclaim valuable space.

To delete them you need to change permissions first:

takeown /F C:\$Windows.~BT\* /R /A
icacls C:\$Windows.~BT\*.* /T /grant administrators:F
rmdir /S /Q C:\$Windows.~BT\
takeown /F C:\$Windows.~WS\* /R /A
icacls C:\$Windows.~WS\*.* /T /grant administrators:F
rmdir /S /Q C:\$Windows.~WS\