Or approach it from a different perspective.

Sort your kit out to what you want on a 100.
Whittle that down to what you think you definitely need on a hundred.
Whittle it down further to what you actually need and meets compliance, nothing else.

Go buy a rucksack that this all fits in but doesn't have much extra space to tempt you to keep adding extras.

Thankyou for your interesting responses. I'll definitely look at smaller sacks - great suggestions much appreciated.

Iain that is very interesting – and gives a scientific explanation for my own observations over the years. However I think the issue for Bridget is not only weight but volume. A good woman's rucksack has a wide comfortable waist band that puts quite a bit of the load on the hips – and of course the shoulder strap should fit comfortably over the shoulders. That is why I mentioned the adjustable back – if you don't get the distance between waist and shoulder straps right no pack will be comfortable. If you don't naturally have much space between waist and shoulders then a very large rucksack either towers above the head or bulges out the sides – or both. It makes you very unbalanced and makes walking difficult. That is why I suggest she looks at a pack with a smaller volume – packed tight it will be far more comfortable that a larger one more loosely packed.

I've just done a backpacking trip with tent and cooking gear, my first with the latter two for some years, and spent most of it noticing the weight of the otherwise comfortable pack (a nearly new Berghaus 65 Trailhead). A couple of days in I worked out the ratio of pack weight (initially 35lb, reduced quickly) to my body weight (initially 135lb, reduced less gradually), and was confirmed in my belief that at more than 26%, it was too high.

So what is the ideal pack to body weight ratio, and, with modern lightweight backpacking gear, how little capacity is it now reasonable to expect a pack to be capable of holding ?

On the first question, it has generally been assumed, and advice given accordingly, that the lighter a person is the less weight it is reasonable for them to be able to carry. A maximum comfortable pack to body weight ratio was thought to be around 20%, so that a person weighing 112lb or 8 stone would have difficulty carrying a pack weighing much more than 22lb, and someone (me) of 135lb (9.5 stone) shouldn't tote more than 27lb. But a 2014 study* by Michael O'Shea of Outward Bound, Kansas State University, proposed that, when factors such as muscle strength and body fat are taken into account, smaller [and lighter] hikers could carry heavier loads than their larger [and weightier] compatriots.

This, according to O'Shea, is because hikers have to haul not only the weight of their pack but their own body weight, so that the heavier you are the more work you have to start doing even before you bend to pick up the rucksack. (As the size of an animal increases, says O'Shea, strength increases more slowly than body weight, so that while ants can carry disproportionately heavy loads, elephants manage relatively small ones.) Using his ‘pack plus body weight' model, he calculated that while an 112lb (8 stone) person could cope with a whopping 50lb backpack (43% body weight), a bulky 243lb (17.3 stone) hiker might carry only 34lb or just 14% of their own weight. So, on this model anyway, I'm a wimp, and Bridget's quite right to be looking at 70litre packs - but not for Hundreds.

On the second question, of decreasing gear weight per item vs pack capacity, it may now be true that a 70litre sack stuffed with lightweight chargers and other modern essentials (including, now, spare face masks) weighs the same or less than the smaller ones which we toted in the 70s, 80s or even 90s. This would need a historical perspective, or maybe fetch your old gear from the loft and try cramming it all into the new pack. But don't forget to take account of your own body weight before you get on the scales with that 70s A-frame.

Iain

* �Backpack Weight and the Scaling of the Human Frame," by Michael O'Shea, The Physics Teacher, October 21, 2014.

Bridget are you sure you need 70l ? - that is a very big rucksack. I am 5"1 and (I must confess) some what heavier than you but not a great deal. I can backpack carrying tent, sleeping bag, stove, cooking gear, fuel, waterproofs spare clothes etc. etc and enough food and fuel for 4 or 5 days using a 50 - 55l rucksack. I had a very ancient and comfortable Berghaus which that had an adjustable back. It has eventually fallen to pieces. Like you I tried a rather expensive Osprey one that I didn't get on with and have gone back to Beghaus with a Women's Trailhead 50 which also has an adjustable back and is relatively light, cheap and very simple. It is a generous 50l but there is also a 60l version.

I'm looking for advice from any long distance walkers who are my height (5'5) and small build (8stone) who have found a comfortable , well fitting, lightweight rucksack (needs to be about 70l capacity) and carried it for at least 12 miles a day without discomfort.
I've had two now, both fitted in the shop but neither have been a success. The latest, an Osprey was expensive and quite heavy before you put anything in - sadly it didn't fit well enough.
Any shared advice, suggestions or experiences from other ladies are most welcome.

Never done a 100 but I use a Montane featherlite 30 ltr pack for most of my day walking , at 710 grams its lightweight enough , there is a 23ltr version at 652 grams , but i find the extra capacity useful especially in winter when extra gear is needed .
Ps anybody had any experience of the daypack advertised in the LDWA shop ? .

I use a Berghaus 640. Very lightweight, 6 mesh pocket's, different size's 2 on the waist band.
Most likely out of production now, but a great bag,worth checking their updated version if there is one.Carries required 100 gear with ease + drink & still feels light.
Need to renew myself.

I generally use a 30 litre bag. The extra capacity is useful for additional clothing in event of really bad weather conditions.

In addition to a waist belt, an adjustable chest strap is very useful for stability and comfort. I prefer simplicity in design, but at least one secure zipped pocket (for small items) and elasticated mesh side pockets (for drink bottles, bars etc) are needed.

In my view, you need some back support and cushioning (most ultra light runners bags skimp on this, and are uncomfortable for long events) But avoid "open cell foam" cushioning in the back, because when the rucksack gets wet it absorbs a lot of water and is heavy. I agree with Elton that rain covers don't really work well in prolonged wet conditions. There are few truly waterproof rucsacks.

You get what you pay for. Cheap bags are not made of very durable material , well designed or well made, and the zips can break or jam. There are lots of good manufacturers out there ( Lowe, Berghaus, Osprey, Vaude etc)

A 20 to 25 litre pack is about right in my experience. I always use a Platypus water system to make sure I drink enough water. I have a 25L Lowe alpine pack which is fine, but is a touch narrow when the Platypus is full. Do make sure you get one with a padded waist strap. The pack I used for my first Hundred only had a thin strap and I finished with a painful weal round my waist.

Your instincts are right: minimum size to minimize weight, but 6 litres is perhaps too small (though some seem to get by with bumbags that size.) I use a 25 litre runner’s pack (Lowe Alpine) weighing about 750 grams. It works well, though it’s not waterproof and the lid pocket is too small.

I use a plastic bag inner, well folded over at the top. I check for waterproofness by inflating it first. I don’t bother with an outer cover. In heavy rain the water will always get in via the shoulder straps and back.

I’ve used a Regatta Packaway jacket for three years and on three Hundreds (including in the downpour on the first night of the Heart of Scotland) and found it excellent. It started leaking today, in the (unforecast!) heavy rain in Bucks. Though I’d use a more weatherproof jacket for prolonged heavy rain with wind, as the Packaway doesn’t have the zip cover weatherproofness that my Berghaus jacket has.

I use Dry Sac from Exped to keep the contents of my Rucksack dry. They come in various sizes from XS to XL and you can buy a pack of four sizes from Amazon for £25.

Thanks for the info I'm sorry you didn't finish but the weather was awfull . I bought a full set of waterproofs prior to the event purely for the weight and size of my bag as I thought surley It can't rain in London as of my previous London marathons , I was wrong . They was regatta pack away 2 , I thought once it stated raining on Saturday night it would be a matter of time before they leaked . They held up all they way including Sunday afternoon and night deluges . Highly recommend them and a bargain price

I used a medium sized pack (Wilderness 35 litre - kind of like this one but not quite, they must have changed the design since I got mine: http://www.action-station.co.uk/outdoor-accessories/rucksacks-backpacks-day-sacks/showitem-GEL-RUC687.aspx); on the one hand the required kit wouldn't have fitted into anything much smaller, but on the other I didn't want to be carrying a full size pack for 48 hours. Despite coming with a supposedly waterproof cover, it couldn't cope with the amount of rain we got on the Saturday night, and most of the contents were soaked. I didn't finish, but I don't think I can blame the backpack for that.

Just wondering what size and make the majority use for the 100 . This year at my first attempt at the distance I had a small backpack rammed solid with the required kit a d little room for anything else . It proved a nightmare to retrieve anything but the weight was very light . It was a vango sprint 6tl . I would appriate responses so I can get it right for the camel teign