I have found that stranded 14 AWG THHN is 6.258 sq mm, but I am having a hard time finding the value for solid 14 AWG THHN. I keep seeing 2.08 sq mm, but I find it hard to believe that the cross-sectional area of stranded THHN is ~3 times larger than solid THHN.
BTW, I am using these figures to calculate maximum conduit fill as allowed by the NEC specs. If you are interested, I have created a conduit fill calculator using Google Sheets. You are more than welcome to use it. Just make a copy of the spreadsheet first.