How to measure penis

Right so a girl I'm talking to has recently asked how big I am down below, however, I have never measured before so I haven't replied. I've now set out the task to measure it but I keep getting different measurements depending on where I place the ruler.

Along the top: 14cm
Along the side: 17cm
Along the underneath: 12.5cm

Guys, if you was to measure your junk how would you do it and to everyone (guys & girls) what measurement do you think I should tell her?

Reply 1

Anonymous #1

These measurements are when erect btw.

Reply 2

unprinted

The classic measurement is along what you're probably calling the underneath - the side you look down on when it's erect and you're standing up - because there are two obvious end points: the very end of the penis and where it makes an angle when it joins your body.