The researchers used satellite imagery to assess how the density of trees is related to local characteristics such as the climate, vegetation, soil conditions and the impacts of human activity, and used the information to build models for the number of trees in various regions.
The global map generated suggests there are around 3.04 trillion trees, or around 422 for each person, on Earth.
A country-by-country breakdown reveals there are more than three billion trees in the UK, or around 47 for each Briton, while in Ireland there are some 709 million trees, equating to 154 for each person.
The highest densities of trees are found in the forests of the sub-Arctic regions of Russia, Scandinavia and North America, but the largest forest areas were in the tropics, which are home to around 43 per cent of the world's trees.
The information on tree populations will help efforts to model global systems such as carbon storage, the changing climate and the distribution of animal and plant species, the researchers said.
Lead author Thomas Crowther, post-doctoral fellow at Yale School of Forestry and Environmental Studies, said: "Trees are among the most prominent and critical organisms on Earth, yet we are only recently beginning to comprehend their global extent and distribution.
"They store huge amounts of carbon, are essential for the cycling of nutrients, for water and air quality, and for countless human services.
"Yet you ask people to estimate, within an order of magnitude, how many trees there are and they don't know where to begin," he said, adding he was "certainly surprised" to find the estimate was in the trillions.