My brother is on a Jetstar flight from Christchurch to Wellington and the allowance is 20kg. The question is - is the weight limit limited to a single checked bag, or can you use more than one bag, as long as it's under 20kg total weight?
From the Jetstar baggage help page:
Your baggage allowance is given by combined weight, not by number of bags. As long as your bags have a combined weight within your allowance, bring as many as you like. No single bag can weigh more than 32kg
So, as long as your brother stays under 20kg total, he's fine with no matter how many bags. The 32kg per bag limit would only matter if he was in business, and/or bought extra luggage allowance.
The answer came at the airport - and it's yes, Jetstar limits by weight, not by number of bags.
At check-in, you're simply asked how many bags you're checking solely to print out the baggage tags. The total is then weighed (if at all) and as long as your total is under 20kg, which his was, then everything works just fine.