Wainwright had it 14.75 miles to the A628 in his Pennine Way Companion. The Trailblazer guide, 2004 edition, shows it as 16 miles to Crowden. I wouldn't have thought that the flagstones made much difference in mileage but certainly it made it easier underfoot. If staying at the youth hostel then 18 miles may be about right as I recorded 17.2 miles from there.