I have Indian 1 Anna coins from 1912, 1940, 1945 and 1946.
According to the data here on Numista they’re all slightly different sizes. But by my measures and eye (having stacked them on top of one another), they appear to be the same size.
I make it 20.5mm for each (though admittedly my callipers are only cheap).
Does the size data here come from mint records or just user submissions?
The diameter data comes from user submissions, and I often find inaccuracies too. I think that the shape of these coins make them especially prone to error.
The Numista guidelines say that the maximum diameter of each coin should be used. So, for example, the square 2 cent coins of Swaziland should be measured from corner to corner. Errors in this measurement on the scalloped 1 Anna coins could account for the variation between the Numista records.
