You can download free excels dumps of every zip code

http://federalgovernmentzipcodes.us/That will allow you to geocode your zips.

Then you can wake up sleeping Pythagoras from 2,500 year ago who will answer your question.

// In the USA, the typical distance between integer Longitude lines is about 53 miles. (these are the east / west coordinate)

// They are further apart at the equator (69 miles) and approach zero at the North Pole.

// but we have few courses at the north pole or the equator, so lets just call it 53.

// In the whole world, its 69 miles between integer Latitude lines.

// With credit to Pythagoras, we know that for a right angle triangle A^2 + B^2 = C^2. I will use (A^2 for A squared)

// We want to find the length of the C diagonal where A is the North South distance and B is the West East Distance

// Let LA1 be the LAtitude 1

// Let LO1 be the LOngitude 2

// Let LA2 be the LAtitude 1

// Let LA2 be the LOngitude 2

// So C^2= A^2 + B^2

// C = SQRT (A^2 + B^2)

// C = SQRT ((69*(LA1-LA2))^2 + (53*(LO1-LO2))^2)

// note that to take a square root you raise it to the power of 1/2 or 0.5

var number OriginLat = [Patient Zip Code - Latitude];

var number OriginLong = [Patient Zip Code - Longitude];

var number DestLat = [Consultant Zip Code - Latitude];

var number DestLong = [Consultant Zip Code - Longitude];

var number Distance =

Round(

((69*($OriginLat - $DestLat))^2 + (53*($OriginLong - $DestLong))^2)^0.5

);

If($OriginLat =0 or $DestLat=0,0,$Distance)