This calculator is based on equations presented by Brian C. Wadell in his book title "Transmission Line Design Handbook".
These equations take metal thickness into account, which must therefore be specified. Typical values will be in the range 20-40um.
Good accuracy (better than 1% error) can be expected, comparing favourably with results from Agilent ADS.
Stripline is essentially non-dispersive, so this calculator is suitable for most circuit types.