The quake was earlier thought to have caused waves 36ft (11m) high
The tsunami that killed more than 200 people in the Samoan islands and Tonga in September was twice as tall as the buildings it hit, scientists say.
The wall of water towered 14m (46ft) and included as many as three major waves, researchers have found.
The waves were caused by a magnitude 8.0 earthquake under the sea.
New Zealand's National Institute of Water and Atmospheric Research has been studying the tsunami to help guard against future events.
A team of scientists under NIWA spent two weeks in the field and found the second of two to three significant waves was said by witnesses to be larger.
The delay between the earthquake and the arrival of the first wave was about 10 minutes in Samoa and 20 minutes in American Samoa, the NIWA scientists said.
It was also very clear that plants, trees, and mangroves reduced flow speeds and water depths over land - leading to greater chances of human survival and lower levels of building damage.
"The same thing will be true in New Zealand as in Samoa: solidly constructed buildings which are appropriately located will survive much better than flimsy buildings right on the beach," said Dr Stefan Reese of NIWA.
"It's also clear that practices such as flattening sand dunes or removing beach vegetation would increase the potential for tsunami damage."
The massive waves that struck Samoa, American Samoa and Tonga totally destroyed traditional wooden buildings, many of them single-storey, along the coast.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.