From the rise time of a signal, get its bandwidth and knee frequency and the trace length above which reflections matter. Longer traces need controlled impedance and termination.
Bandwidth. For a 10–90 % rise time tr, the 3 dB bandwidth of a single-pole response is BW = 0.35/tr. The knee frequency, above which the spectrum of a digital edge falls off quickly, is fknee = 0.5/tr.
Critical length. A trace behaves as a lumped connection while its delay is short compared with the edge. The calculator uses the common rule that a line longer than one sixth of the edge length needs to be treated as a transmission line: Lcrit = tr·v/6, with v = c/√εeff. Some guides use a quarter or a half instead of a sixth, which gives longer limits.
Reflections and crosstalk depend on how fast the edge changes. A slow clock with fast edges needs the same care as a fast clock.
For a stripline use the dielectric constant of the material. For a microstrip it is lower, about 3.0 to 3.4 on FR-4. The microstrip calculator gives the exact value for your trace.
Delay of a trace, maximum length mismatch for a skew budget, and wavelength on the board.
Near-end and far-end crosstalk between two parallel traces, from the coupled-line impedances.
Width a trace needs for a current, or the current a trace can carry, with IPC-2152 and IPC-2221.
Impedance of an outer-layer trace over a plane, with solder mask or embedded, and width for a target impedance.
Impedance of an inner-layer trace between two planes, symmetric or offset, and width for a target.
Differential, odd, even and common-mode impedance of edge-coupled microstrip and stripline pairs.