The geometric mean radius factor depends on the construction of the conductor, the number of stranded wires and the compaction of the strand.

The IEC 60287-1-3 Ed.1.0 Table 1 lists values factor K

• Values in the standard are for 1 (solid), 3, 7, 19, 37, 61, 91, and 127 number of wires, the other values are interpolated.
• The given values are applicable to non-compacted circular conductors.
• The equation for a single solid wire is $\exp(\frac{-1}{4})$ being equal to 0.77880078...
• For compacted conductors the value for solid conductor is used (0.7788).
• Values for hollow conductors are dependant on the inner and outer diameter of the conductor as by example in annex B of the the IEC standard.
• No information was given for shaped conductors, the same values are taken as for non-compacted circular conductors.

Symbol
$K_{GMR}$
Used in
$GMR_c$
Choices
Number of wiresfactor K
10.7788
30.678
60.714
70.726
120.739
150.747
180.755
190.758
300.764
340.766
350.767
370.768
470.77
530.771
580.772
610.772
910.774
1270.776
1690.777
2170.778
2710.7785