Finnair has started weighing its passangers before they board flights in Helinksi, but it's not an exercise in fat-shaming.

The Scandanavian airline is gathering data in the hopes of slashing operating costs, so it can better estimate fuel requirements. Currently, like most other airlines, Finnair uses average weight estimates from the European Aviation Safety Agency (EASA) - a report compiled eight years ago.

This data may be in need of an update, Finnair reckons, so it's collecting its own.

The program, carried out during check-in at Helinski Airport, is entirely voluntary and so far the carrier has got 180 passengers to step onto the scales. The target is 2,000, after which it hopes to have a more streamlined approach to fuel estimations.

"Airlines know what the aircraft weighs, what the check-in luggage weighs, but not what passengers weigh," Finnair's communications director Paivyt Tallqvist told the BBC.

What are the current figures?

The EASA estimates that the average male weighs 84.6kg, a female 66.5kg and an under-12, 30.7kg.

That's pooling the entirety of Europe, however. Reliable up-to-date figures for Finland are hard to come by, but according to Channel News Asia, the average Finnish man weighs 85kg and the average Finnish woman weighs 70kg.

And this isn't taking into consideration the varying seasons. Big coats and heavy boots during winter add to the load, wheras during the summer the opposite is true.

Has this happened before?

Yes. Last October, Hawaiin Airlines carried out a six-month survey of the same nature.

A Hawaiian Airlines spokeswoman told Telegraph Travel: "Over time our fuel burn on Pago Pago flights was consistently much higher than projected, indicating that our weight assumptions were inaccurate.

"We review weights on any flight within our route network that demonstrates such a discrepancy. For example, we surveyed our Japan and Korea flights in 2015 and our new Narita flight earlier this year."

In August 2015, Uzbekistan Airways did the same thing.

"According to the rules of International Air Transport Association, airlines are obliged to carry out the regular procedures of preflight control passengers weighing with hand baggage to observe requirements for ensuring flight safety", the company said at the time.

In 2013, Samoa Air became the first airline in the world to charge passengers according to their size. Those flying on the South Pacific carrier, which is no longer in operation, were asked to pay one Samoan tālā (around 29p) for each kilo that they, combined with their luggage, weighed.

It is worth noting that Samoa, according to the CIA’s World Factbook, has one of the highest rate of obesity in the world. More than two-thirds of its adult population are considered obese, it says, which might have been the reason behind Samoa Air's then-controversial system.

Why is weight so important to airlines?

The total weight of a plane, including all its passengers and cargo, is estimated before every flight to work out how much fuel will be required. Naturally, the heavier the plane, the more expensive the journey in terms of fuel, but safety comes into it too.

All aircraft have a maximum take-off weight. A Boeing 747's maximum, for example, is in the region of 443 tonnes, depending on the model. The weight of a plane can then be affected by a number of other factors, the weather being one of them.

In June of this year, around 40 flights were cancelled at Phoenix Sky Harbour International airport after the mercury soared to 49C, making some planes unable to take to the skies. Hot air, being thinner than cold air, throws off the calculations relating to weight and climb gradient, rending some of the planes too heavy to take off safely.

