All you need to know is:

C C# D Eb E F F# G Ab A Bb B and back to the beginning:

Count how many frets up the neck you're capoed at. Count up the same number on the list above, e.g. if you're capoed at the fourth fret and playing in E shapes, start from E on the list and count up four, and you're playing in the true key of Ab. If you're capoed at the fifth aand playing in D shapes you're in G

Hope this helps