It seems a lot more natural to define pi by the ratio of the circumference of a circle to the radius, rather than to the diameter. The diameter is hardly ever used in math (at least in my experience), and it seems like most formulas involving pi involve the combination 2pi. Is it a historical accident that we use pi=C/d, or is there a good reason for it?(adsbygoogle = window.adsbygoogle || []).push({});

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Why does pi=C/D and not C/r?

**Physics Forums | Science Articles, Homework Help, Discussion**