google metric calculator?

I want to make some conversions in my app to convert, let's say feet to km, gallons to liters, etc开发者_如何学运维. I really like how does google handle this kind of conversion requests.

do they have any API to use it?

I've found examples on how to convert currencies with google using google's undocumented API. I'm not looking for the currency conversion rate, I want to have just a basic metric <-> imperial conversion, based on the input

any help would be appreciated!

Thanks!