Finding the IBU's of any herb

Ive been searching around for a few hours and haven't found anything on the subject so now I'm asking. How can I find the IBU rating on any herb? Normally I use damiana as a bittering herb, but to make different brews I would like to now how much it bitters.

IBUs are based on the alpha acid bittering compounds in hops. While other botanicals may provide bittering of some sort I don't think it is going to translate or cross reference to what humulus lupus does to beer.

BigEd said:

IBUs are based on the alpha acid bittering compounds in hops.

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And the oxidized beta acids, and (at much smaller levels) other compounds.

While other botanicals may provide bittering of some sort I don't think it is going to translate or cross reference to what humulus lupus does to beer.

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I agree. IBU estimation is kind of a black art anyway, even when limited to hops that have known, measured levels of alpha/beta acids--heck, most of the formulas used by home brewers to estimate IBUs completely ignore beta acids even though those are certainly part of true measured IBUs.

Even measured IBUs don't capture anywhere near all bittering compounds, and I'd expect that most botanicals that provide bittering aren't contributing true IBUs even when they are providing a similar impact on flavor.