Finnish carrier Finnair has begun weighing passengers with their carry-on luggage as part of a study aimed at better determining the weight of the aircraft before take-off, it said Wednesday.

The weigh-ins will take place in February, April and May and are on a voluntary basis, it said.

"Measurements began at Helsinki Airport this week on Monday... So far, more than 500 volunteer customers have participated in the weigh-ins," Finnair spokeswoman Kaisa Tikkanen told AFP.

Finnair noted in a statement that flight balance calculations require airlines to know the "weight of the aircraft itself and the weight of fuel, checked baggage and cargo, onboard catering, water tanks, and of course customers."

Airlines may use average weights provided by aviation authorities or collect their own data, it said.

"The collected data is not linked in any way to the customer's personal data," said Satu Munnukka, head of ground processes at Finnair.

"Only the customer service agent working at the measuring point can see the total weight, so you can participate in the study with peace of mind," she said.