How Fast Is Steel Rusting?

Bare steel in humid air loses roughly 0.1 mm per year to rust — a relentless chemistry of iron returning to its mineral state. Structural steel bridges and ships shed millimetres over decades, which is why painting them never really stops.

The Eiffel Tower needs repainting every 7 years just to stay ahead of rust.

• About the same pace as fingernails growing
• 30× slower than the wound on your finger heals