More than 100 experts analysed data from 1170 surveys to come up with the figures, highlighting the extraordinary scale and diversity of the Amazon rain forest.
The vast size and difficult terrain of the Amazon Basin has historically restricted studies of tree communities to a local or regional level, making it difficult to see the "big picture". This lack of information about Amazonian flora on a basin-wide scale has hindered science and conservation effort.
"In essence, this means that the largest pool of tropical carbon on Earth has been a black box for ecologists, and conservationists don't know which Amazonian tree species face the most severe threats of extinction," said research author Dr Nigel Pitman, from The Field Museum in Chicago, US.
The new findings, published in the journal Science, provide the first estimates of the abundance, frequency and distribution of many thousands of Amazonian trees.
Extrapolating the data, compiled over 10 years, suggests that greater Amazonia harbours around 390 billion individual trees, including Brazil nut, chocolate and acai berry.
The area covered encompasses the Amazon Basin (including parts of Brazil, Peru, Columbia) and the Guiana Shield (Guyana, Suriname, and French Guiana), spanning an area roughly the size of the 48 North American states.
"The most common tree species in the Amazon now not only have a number, they also have a name," said co-author Dr Hans ter Steege, from the Naturalis Biodiversity Centre in the Netherlands. "This is very valuable information for further research."
The study also offers insights into the Amazon's rarest trees with about 6000 species having fewer than 1000 specimens.