to be precise,
@rjack321 is correct and assuming both are Fabers, they are identical in internal volume and as such are identical tank factors and will always hold the same volume of gas when filled to the same pressure, regardless of what that pressure is...
No one wants to remember the Z-factor when using low pressure tanks. That also means that the CF/100psi is higher when at low pressure than it is at high pressure by about 3% at 3000, 5% at 3442 working pressure, and 6% at 3600psi cave fill with percentages being applicable to air fills only at roughly room temperature.
Now, since we are being pedantic.
Faber LP108=FX133=17.0L
PST LP104=HP130=~16.6L *this sticks in my head for some reason, but they are a noticeably shorter than the Faber equivalents*
Worthington LP108=Faber LP108=17.0L
Worthington HP130<PST HP130=16.0L
You get to decide if that is significant enough of a difference.
100psi=6.9bar
16L=.565cf ->3.9cf/100psi
16.6L=.586cf ->4.0cf/100psi
17.0L=.6 ->4.14cf/100psi
Use 4cf/100psi/1.06=3.75 to account for full fill or straight 4cf on the bottom, the
+3% is less than the precision of your pressure gauge.