# Capacitance of loops

1. ### csopi

79
Hi,

Does anybody know a nice formula for the capacitance of two metallic wire loops with equal radius R?

(The center of the loops are above each other, their distance is d. The whole system is in vacuum)

Thank you!

2. ### the_emi_guy

593
There will not be a nice formula for that.

If you just need the capacitance value of a specific geometry you can use the free field solver at http://www.fastfieldsolvers.com/.

3. ### CWatters

Can you assume the radius R is >> d ?? In which case isn't this just the same as two parallel wires?

4. ### csopi

79
CWatters: yes, in that case it would be just two parallel wires. However I was looking for a general formula, that works when R ~ d as well. Actually, I'm trying to estimate the capacitance of a coil, because when you have a coil made of thick wire and you have just a few turns, it cannot be negected in general.

the_emi_guy: thank you very much for the software. It seems rather professional. It'll take some time to learn how to use it though.