Excel - As-the-crow-flies distance function

MS Excel 'standard' formula

Given the following input fields (in degrees): From latitude (cell A2), From longitude (cell B2), To latitude (cell C2), To longitude (cell D2), the formula is

=IFERROR(ACOS(COS(RADIANS(90-A2))*COS(RADIANS(90-C2))+SIN(RADIANS(90-A2))*SIN(RADIANS(90-C2))*COS(RADIANS(B2-D2)))*6371;0)
Dependent on your MS Excel setting you may have to replace the semicolon by a comma.

Alternative user defined function: MS Excel VBA code to be put in a module

Note: in general, a user defined function will execute slower than a standard function, which can become a disadvantage in case of a large amount of formulas.
In MS Excel, press Alt+F11 to open the Visual Basic Editor (Windows). Via top menu: Insert → Module. Copy the MS Excel VBA code below into the module.

Public Function globeDistance(LatFrom As Range, LonFrom As Range, LatTo As Range, LonTo As Range) As Double Const Pi = 3.14159265358979 Const R = 6371 Dim dLat As Single, dLon As Single, lat1 As Single, lat2 As Single, a As Single lat1 = LatFrom * Pi / 180 lat2 = LatTo * Pi / 180 dLat = (LatTo - LatFrom) * Pi / 180 dLon = (LonTo - LonFrom) * Pi / 180 a = Sin(dLat / 2) * Sin(dLat / 2) + Sin(dLon / 2) * Sin(dLon / 2) * Cos(lat1) * Cos(lat2) globeDistance = R * 2 * WorksheetFunction.Atan2(Sqr(1 - a), Sqr(a)) End Function