Trace on top of dielectric, ground plane below.
Used for outer-layer signal routing.

Formula (IPC-2141A):
Z₀ = (87/√(εr+1.41)) × ln(5.98H/(0.8W+T))

Trace is covered by a dielectric layer above (e.g. soldermask or prepreg). Ground plane below.

Formula:
εr_eff = εr × (1 − e^(−1.55 × B/H))
Z₀ = (87/√(εr_eff+1.41)) × ln(5.98H/(0.8W+T))

Trace is embedded between two ground planes, centred in the dielectric.

Formula (IPC-2141A):
Z₀ = (60/√εr) × ln(4B / (0.67π(0.8W+T)))
where B = distance between ground planes.

Two coupled microstrip traces. Differential impedance is the impedance seen between the two conductors.

Formula:
Zdiff ≈ 2 × Z₀ × (1 − 0.347 × e^(−2.9 × S/H))
where Z₀ is single-ended microstrip impedance.

Two coupled traces embedded between ground planes.

Formula:
Zdiff ≈ 2 × Z₀ × (1 − 0.347 × e^(−2.9 × S/B))
where Z₀ is single-ended stripline impedance.