Ask HN: Is there an RFC for weights and measures?

Reading RFCs is well outside my wheelhouse, but I'm curious if there is anything like RFC 3339 (Date and Time on the Internet: Timestamps), but directed at establishing a common lingua franca for weights and measures. Is this even something the IETF would concern themselves with? Are timestamps such a unique case that this isn't even a concern.

I ask because there are standard date/time format strings, so I wondered if the same is true for weights and measures. I'd like to build a JS lib that handles this, so it'd be pretty nice to know if there's already a standard expected API outside of just what the Imperial and metric systems give us.