But the Samoan airline's policy is being attacked by an obesity expert and community leaders as insensitive and lame.
Samoa Air is a national airline which flies between the country's two main islands, Upolu and Savaii, and has started flights to American Samoa and Tonga.
Passengers pay a price per kilogram they weigh, and the price varies according to the length of the route.
The rates range from 1 tala (NZ52c) a kilogram - for the weight of the traveller and their baggage - on the airline's shortest domestic route to 3.8 tala ($1.98) a kilogram for travel from Samoa to neighbouring American Samoa.
The airline, established last year, says the fare system is helping people understand the issue of obesity.
Chief executive Chris Langton said it was fairer than standard fares, and that some families with small children were now paying substantially cheaper fares.
"This is the fairest way of travelling," he told ABC Radio. "There are no extra fees in terms of excess baggage or anything - it is just a kilo is a kilo.
"When you get into the Pacific standard weight is substantially higher [than in south-east Asia] but it can be quite diverse. People generally are becoming much more weight conscious. That's a health issue in some areas. It has raised the awareness of weight."
But New Zealand-based Fight the Obesity Epidemic spokeswoman Dr Robyn Toomath said the policy was disgusting. "I think that's absolutely appalling. It's a stigmatisation of people and really just powerfully discriminating."
It was unfair of the airline to suggest it was the passenger's fault they were obese and it was of no help in the cause against obesity.
"That is a dreadful lack of understanding. There are many things that cause obesity ... they're suggesting that it's the person's responsibility and that they have control over it, when in reality there are other factors."
Auckland-based Samoan community leader Teleiai Edwin Puni said he understood weight was a crucial factor on aircraft.
"I weigh 200kg. I would be okay to pay the fare, provided it's reasonable. But I don't think it's a good excuse saying that they're trying to promote healthy living - that's a lame reason."
Mangere MP Su'a William Sio said that had it been an airline in New Zealand, people would be up in arms. But most people in Samoa would probably accept the fares.
Pacific Island nations have some of the world's highest rates of obesity.
Mr Langton believed charging by weight was the concept of the future.
"As any airline operator knows, airlines don't run on seats, they run on weight."
Air France and Dutch airline KLM caused protests when they said in 2010 that anyone with a waistline of more than 135cm would have to book a second seat on their aircraft.
- Vaimoana Tapaleao of the New Zealand Herald
