If you want an accurate way of measuring your walks then I'm afraid a GPS is the way to go - they're not cheap, but you get a hell of a useful piece of equipment for your cash.
I own a Garmin eTrex Summit, which I keep strapped to the top of my rucksack. At any point in my walk I can see how far I've walked, my top speed, average speed, trip time, altitude gained/lost etc. etc. :- plus I'm secure in the knowledge that I can get a read out ( in Lat/Long or OS co-ords ) of my position, which is accurate to less than 20 feet . . ..
When I get home I can then upload the data to MemoryMap on my PC -where I get to see a highly accurate track of my walk overlaid on both an OS map and an aerial photo . . . The built in elevation data will also allow me to plot a profile diagram of my walk, showing all the ascent and descents of the walk . . . .