it's a little trouble to calculate it.
You can divide the length into 10 segments, and setup models, then calculate GD(group delay) or lamda, then you know electrical length.
I divided 50cm into 10 segments, each is 5 cm. So use 11 shunting 2pF caps and 10 series 0.5uH inductors.
The system group delay is 2.278ns, so the electric length is 0.068 lamda.