There is no minimum length, Airlines typically have belt around 40" to 50" in length but some carriers with regular oversize pax have fitted longer ones.
Alaska Airlines for example have 46" belts.
Some airlines will provide larger pax with extension belts of around 20-25" but you can no longer use your own extender at least in FAA land.
Last edited by Fargoo; 12th Mar 2013 at 23:59.