The Wet Tropics World Heritage Area (WTWHA) directly generates almost $426M worth of tourism per year, according to research released in Cairns.

The figure was a conservative one, said James Cook University's Dr Fay Falco-Mammone, lead researcher on a project that surveyed 861 international and domestic tourists.

"Our calculations are based on visitors' direct expenditure, with none of the multipliers sometimes used to estimate broader economic impact," she said.

"We also focused purely on tourists, so the figure doesn't include expenditure by locals visiting their favourite spots."

Visitors were surveyed on factors including which sites they visited and for how long, the duration of their holiday, their expenditure and their planned budget for the trip.

"We calculate that expenditure involved in visiting the World Heritage Area accounts for 21.8% of the $2 billion total spent by visitors to the region," Professor Prideaux said.

"More than 910,000 visitors stay on average for just over three days in the World Heritage Area, spending an average of $147.41 per day."

The research, published by the Rainforest Cooperative Research Centre, is based on visitor surveys conducted at Lake Barrine, Mossman Gorge, Skyrail and the Marrdja Boardwalk in the Daintree.

"Because access to the Wet Tropics World Heritage Area is substantially free, that makes its economic contribution a difficult one to calculate," Dr Falco-Mammone said.

"But that also makes it an important value to calculate, because when assets are free they can be in danger of being undervalued."

The estimate produced by Dr Falco-Mammone and Professor Bruce Prideaux is $49M higher than the previous evaluation by researcher Sally Driml in 1997.

"The studies are not directly comparable, because of differences in the methods used," Dr Falco-Mammone said. "One of our aims has been to design this study in such a way that it can be used as a baseline for future comparisons, which will assist with planning in the tourism industry and management of the World Heritage Area."