Research has quelled fears that millions of animal and plant species will be extinct before they are actually discovered.
Scientists from Auckland University, Griffith University in Queensland and Oxford University in England say there are between two and eight million species - of which 1.5 million have already been discovered and named.
Earlier estimates of the number of species have been as high as 100 million. In 2011 the PLoS Biology journal published an analysis suggesting there are 8.7 million species, give or take 1.3 million.
Associate Professor Mark Costello of Auckland University and his colleagues now put the top figure at eight million, in research published on Friday by Science magazine.
"Over-estimates of the number of species on earth are self-defeating because they can make attempts to discover and conserve biodiversity appear to be hopeless," Dr Costello said.
"Our work suggests that this is far from the case. We believe that with just a modest increase in effort in taxonomy and conservation, most species could be discovered and protected from extinction."
AAP reports that while the research suggests that species are more likely to be discovered than go extinct, the authors do not underplay the threats to species and their habitats.
The combination of over-hunting, habitat loss and climate change mean that extinction rates could increase rapidly in the future.
Dr Costello said discovery and naming of species is critical to their conservation.
"Naming a species gives formal recognition to its existence, making its conservation far easier," he said.