effective core parameters

Hello,
I need the formulae for computing the parameters of a POT core, such as "effective magnetic path legth, le" and "effective cross sectional area, Ae".
I know I have to find C1 = Σ(l/A) and C2 = Σ(l/A2). And then to calculate le = C12/C2, Ae = C1/C2. But I need the exact formulae for C1 and C2.
I know also that all of these formulae are described in IEC60205.

Thanks in advance for the time spend to answer.

Regards
Zdrav