Most VHS tapes are called T120.
Which can hold up to 6 hours.

You can also buy T160 tapes.
These can hold up to 8 hours.
The tape is thinner, so it holds more tape.

If the tapes have their original storage box, it will say T160 on the box.

If you don't have the box or a label on the tape housing, there is no way to tell if it is T120 or T160.