I recently spoke to an older man who still thought that his country (Austria) backs its currency with gold reserves. I consider him a smart man... so I had to check:

Austria has 280 tn of gold in it's reserves. At current prices (116,139 €/kg) that's only 32.5 bn.

M2 of Austria was 520 bn USD or 448Bn EUR.

M1 was ~320 Bn.

So depending on how you measure it the backing is at most 10%.

Still, it's much better than I expected. But bear in mind that gold prices have doubled recently... so a few years ago it was probably below 5%. A far cry from the strict central banking of the post war years, when people still remembered hyperinflation of the 1920's.