Insects and other arthropods are central to terrestrial ecosystems. However, data are lacking regarding their global population abundance. We synthesized thousands of evaluations from around 500 sites worldwide, estimating the absolute biomass and abundance of terrestrial arthropods across different taxa and habitats. We found that there are approximate to 1 x 10(19) (twofold uncertainty range) soil arthropods on Earth, approximate to 95% of which are soil mites and springtails. The soil contains approximate to 200 (twofold uncertainty range) million metric tons (Mt) of dry biomass. Termites contribute approximate to 40% of the soil biomass, much more than ants at approximate to 10%. Our estimate for the global biomass of above-ground arthropods is more uncertain, highlighting a knowledge gap that future research should aim to close. We estimate the combined dry biomass of all terrestrial arthropods at approximate to 300 Mt (uncertainty range, 100 to 500), similar to the mass of humanity and its livestock. These estimates enhance the quantitative understanding of arthropods in terrestrial ecosystems and provide an initial holistic benchmark on their decline.