The type of terrain, genetics, fitness and mental level of indidviduals, footwear, the weather and many more variables need to be factored in.

For me personally, I know that I can walk 7.7 kms (4.6 miles) in 1 hour 5 minutes on concrete with carrying a pack that weighs anywhere from 6 to 20 lbs. I do this at least twice a week walking to and from work which makes a single day total of 9 miles.

Even one way at 4.6 miles, I know that I could not keep this pace for hours on end. At best, perhaps 3-4 hours broken up over a day while the rest of time at a slower pace of perhaps 3 to 4 miles per hour. At this rate, figure on about a 28-30 mile day. Keep in mind that this would be the extreme and that I am better shape then 99% of my contemporaries and I also cycle over 2000 miles per year. How many days could I do walk at this rate? Maybe 3-4 days in a row before the feet and legs start to have problems as walking on concrete with a heavy pack is extremely hard on the bones and muscles.

To take into consideration other people who may be with me. My partner (ex marathoner / tri-athlete / adventure racer), she can keep up with me for a few hours but certainly not for many hours or days. If it was just her and I carrying 20 lb packs, 20-25 mile days are doable on concrete. If the weight of the packs were not a factor then this distance could be exceeded....believe me, I would be on the lookout for the first available baby stroller etc to carry the packs in.

As for other people in the group, my son and daughters who are in their mid teens are no slouches, both are good athletes and I know from previous experience, they are very capable of walking long distances and could probably outwalk us both in the long run (no pun intended).

For others who may be in a group, this includes other fmaily members or most friends, the distance would not be measured in miles, rather in hours. I would suspect that most would be done in by hour 3...even at a slow pace.

Walking offroad on mountain trails, foresty roads etc, this is a totally different matter. Depending on the terrain and weather, the days walking distance can be measured in single digits.

For example, a hike we regularly do in summer takes 2 hours each way over an 6 km (3.6 miles) distance and over some steep terrain. This same hike yesterday took almost double the amount of the time due to the warmer then expected afternoon sun heating up and melted the previously walkable on snow crust that had us falling through up to our knees into slush below. By time we got down off the mountain, my partner and I were tired, wet, sore and hungry. There is no way that this type of walking can be sustained for hours...let alone days on end.

In summer, the most I have covered in a single day in rough mountainous terrain over an elevation gain of 6200 feet is 17 miles...and it just about did me in. On less steep ground, 2 miles an hour is about our average and over a very long day, 20 miles has been done on good trails with pack weights between 25-35 lbs. Over a number of days, these distances would be much shorter with each passing day as this pace cannot be substained carrying any amount of weight.

Lastly, the above is based on our experiences and our physical conditioning. YMMV (Your mileage may vary)....really.