The Salitronic PCB Impedance Calculator is a free online tool for controlled-impedance design. It computes trace width, effective permittivity, loss and propagation delay for microstrip, stripline, coplanar waveguide (CPWG) and differential pairs, using the Hammerstad-Jensen, Cohn and Wadell models. It needs JavaScript and runs in your browser.
Read more about the PCB Impedance Calculator, or see impedance control in high-speed design.