I developed the route card spreadsheet to help me quickly write up and calculate route plans for Scout walking weekends.  A copy can be downloaded from here:

http://www.magpieschest.co.uk/blank.xls

The Grid reference (6-figure) is entered with the first 3 digits in the column (B) the last three in column C.  It then uses vectors from these two locations to work out the bearings and the direct “Crow Fly” (i.e. straight line) distance.  Some sites, such as http://www.sewhgpgc.co.uk/xc/os2.php will allow you to check your six-figure grid references against a Google map.

The measured distance is the more realistic distance between the two points.  You could use the map and measure it, or use an online website like www.mapmyrun.com to calculate it.

The estimated time is based upon the walking speed.  At the bottom is the total “non stop” estimate as well as an additional calculation adding ten minutes for every hour walked.

I included the Naismith’s calculation, but I’m not sure of its accuracy.