42 – on paper, at least. Every fold doubles the thickness. After 42 doublings, 0.1 mm turns into about 440,000 km, more than the Moon's average distance of about 384,400 km.
Every fold doubles
When you fold, the paper stacks onto itself: 1 layer becomes 2, then 4, then 8. After 10 folds there are 1,024 layers, just over 10 cm. After 20 folds, more than a million layers – about 105 metres.
And in real life?
In reality you run out quickly: every bend uses up paper, and the length you need grows explosively. In 2002, Britney Gallivan, a high-school student in California, folded 1.2 km of toilet paper twelve times in the same direction. She had worked out the length beforehand. Until then, more than eight folds was thought impossible.
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