First of all you have to pick up the conductor diameter.
The total cross sectional conductor area is not 100% nominal but 95.5-93% due technological tolerances.
The conductor may be: solid [one single strand] or stranded [7, 19, 37, 61 strands].
Stranded in turn may be compressed, compacted or circular class II stranded.
Let's say the nominal cross sectional area of conductor is 50 sqr.mm [or 1/0 AWG approx.53.5 sqr.mm].
According to IEC60228 the conductor diameter of solid [one single strand] =7.8 mm [only 47.78 sqr.mm]
According to IEC60228 the class II conductor diameter will be 9.1 mm [19 strands].
The conductor diameter for class II could be approximated using formula: dia=sqrt[scu*4/pi()/1.2] mm
scu =nominal cross sectional area [sqr.mm].
compressed will be 0.97*class II dia=0.97*9.1=8.83 compacted 0.9*9.1=8.19 mm
According to ASTM B8-86 class B stranded the conductor diameter will be 0.372 [9.45 mm] compressed =0.361 inches[9.17 mm] compacted =0.336 inches[8.5 mm].