@simone-malvezzi
No, Qt does not supply a set of measurement conversion tables, that's not its job. You could write it yourself, see if there is any pre-written C++ libraries/tables provided, or possibly grab them off the net, either dynamically or statically.

As an aside, you will have to decide how "complete" you want to be. Personally I am great fan of Imperial instead of this Metric rubbish, but even I don't measure in "rods", "poles" & "perches" (e.g. http://www.northcravenheritage.org.uk/NCHTJto2009/Journals/2006/RodsPolesPerches/RodsPolesPerches.html) ;-) Though --- and I'm sure you're fascinated --- in winter I measure temperature in Centigrade but in summer I measure in Farenheit....

Maybe Qt7 ...

I can eventually try also to add an implementation variant for the function “QVariantValueHelper::metaType” (on my own).