Acuity of one's sight is rated on the 20/20 scale. An online search appeared to indicate there is no comparable 'standard' to rate olfactory acuity.
How is acuity of the olfactory system rated?
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One olfactory acuity rating method that has found acceptance in some studies (despite the commercial-sounding name) is based on "Sniffin' Sticks,"
"a test of nasal chemosensory performance that is based on penlike odor-dispensing devices. It is comprised of three tests of olfactory function: tests for odor threshold, discrimination and identification. Previous work has already established its test-retest reliability and validity in comparison to established measures of olfactory sensitivity. The results of this test are presented as a composite TDI score--i.e., the sum of results obtained for threshold, discrimination and identification measures."
In the paper from which this abstract portion was taken$^1$, subjects were assigned a score based on their thresholds, ability to discriminate, etc., and the findings were said to be internally replicable (consistent from one test to the next).
This is probably not the only rating available but it has been used on other studies and seems to be taken seriously by M.D.s and others who measure such things.
There is no absolute measure of olfactory acuity. People are classed as 'anosmic' if they do poorly enough on the test but that doesn't mean they have no sense of smell (although that might be the case). Likewise people who get a high TDI score are--by definition--people who got the "Sniffin Sticks" right. They might be poor at discriminating a good coffee from a bad one based on smell.
The test seems to do what it was intended to do: quantify relative olfactory acuity in a replicable way.
An earlier study is somewhat reserved. From an abstract: "It is concluded that ‘Sniffin’ Sticks’ may be suited for the routine clinical assessment of olfactory performance."
$^1$ Eur. Arch. Otorhinolaryngol. (2000) 257(4):205-11. Multicenter investigation of 1,036 subjects using a standardized method for the assessment of olfactory function combining tests of odor identification, odor discrimination, and olfactory thresholds. Kobal et al.