Calculate Effective Dielectric Constant on FR4 PCB

[likephysics]

While designing a microstrip, how do I calculate the effective dielectric constant if the microstrip is laid on FR4 PCB(er=4).
Whats the formula for calculating effective er?

 

[jsgruszynski]

Your going to hate yourself...

e = e_r * e₀

Sort of like you'd expect.