Formula for Cable size

Back to Engineer, it's star from, when i want to crimp the terminal and take pull of force for thats cable, but i didn't know what size of thats cable, couse the mark on thats cable was blur, not clearly to read, then i remember that to fine the size of cable we can use the formula,..oh i forgot the formula, i ask to my friend via mail, and he call me by phone tell about the formula. and below the formula for Looking cable size.


Example:
we have one cable no identification size,
1. Inner strip the cable
2. Count The wires
3. Measure using caliper 1 pcs of wires/conductor to know the diameter

see below picture:




the formula are:
d² x n x (π/4)
= 0.23² x 7 x 0.785
= 0.290 mm

for make sure what size of cable, you must convert from mm to AWG
Example:
24 AWG = 0.200 mm
22 AWG = 0.324 mm
20 AWG = 0.519 mm

from:Table IPC Standar or www.ipc.org

0.290 mm is closly to 22 AWG size of cable