Weighing individual cells – some of the tiniest things in the world – can require some outside-the-box thinking. “A resisting force is exerted on a body falling through a viscous fluid at rest,” begins a paper, now 70 years old and possibly the first to describe weighing a single, individual cell. Averaging over close to 70 different cells, the weigh-in gave a yeast cell mass of around 79 picograms – that’s 79 trillionths of a gram – with measurements ranging from 24 to 192 picograms individually. Yeast cells are spherical – pretty much the perfect shape for math and physics – but others aren’t so easily geometrized. But scale the size way down, and the precision way up, and “eyeballing it” is a surprisingly effective way to work out how heavy a single cell is.