This is a question you may find yourself asking a little more often now, due to recent political events.
Thanks to an AsapScience explainer video, you don’t have to wonder any longer.
The video says it depends on a lot of factors, but a one megaton nuclear bomb – which is relatively small – could cause first degree burns to everyone in an 11km radius, 2nd degree burns to those in a 10km radius, and third degree burns at 8km.
Picture: Asap Science / YouTube
Third degree burns that cover 25 per cent of the body will likely be fatal, it explains, without urgent medical care.
For a one megaton bomb, within a six km radius, there would be around 180 tonnes of force on the walls of every two-storey building.
The video then explains that, if you survive that, the next problem is radiation, and then the fallout – which can travel for hundreds of miles.
Here's the full video, if you're not already terrified enough: