I remember have heard this long ago on Reddit but was never interested in doing the research needed, then I found it was indeed even more rarer 
Here is what I got:
"The World Gold Council estimates that all the gold ever mined totaled 187,200 metric tons in 2017" so this means there is a total equivalent in ounces of 187200000/0.02835 = 6,603,174,603 ever mined at this point in earth.
So with a total of 21,000,000 that would be ever created this means a total of 6,603,174,603/21000000 = 314 bitcoin ratio against gold, so you can say per one bitcoin there is 314 gold ounces
Links: https://en.wikipedia.org/wiki/Gold_reserve
Here is what I got:
"The World Gold Council estimates that all the gold ever mined totaled 187,200 metric tons in 2017" so this means there is a total equivalent in ounces of 187200000/0.02835 = 6,603,174,603 ever mined at this point in earth.
So with a total of 21,000,000 that would be ever created this means a total of 6,603,174,603/21000000 = 314 bitcoin ratio against gold, so you can say per one bitcoin there is 314 gold ounces
Links: https://en.wikipedia.org/wiki/Gold_reserve
My saliva is even much more rare: Im capable of producing it only about 700 000 ounces in my lifetime. Its also unique, coded with my DNA, no one else can reproduce it.
It is about 30 times rarer, than BTC.