You can trade some accuracy for speed by calculating the straight-line distance and then increasing it by some factor to account for turns and detours. Convert

You can trade some accuracy for speed by calculating the straight-line distance and then increasing it by some factor to account for turns and detours. Converting zip codes to latitude/longitude is a trivial process if you have a database (e.g. MaxMind) or API (e.g. SimpleGeo). You can calculate straight-line distance between two lat/lon pairs pretty easily (http://jan.ucc.nau.edu/~cvm/latlon_formula.html http://jan.ucc.nau.edu/~cvm/latlon_formula.html), and then pad this number to account for geography (e.g. 20 miles as the crow flies is ~27 miles driving). If you can sacrifice even more accuracy, you can use 50-70 miles per degree latitude/longitude and just find results within a certain range of a given lat/lon pair.