Start with capacity – everyone needs a place to start and we think capacity is that place – to some extent it will define what you are going to use the pack for and how much weight you are going to carry – a 60+ litre rucksack will surely be a backpacking rucksack – whereas a 10 litre pack will most likely be for running or fast ascents.

Often the most reliable way of determining the size you need is to compare it with what you have now, so, if you currently have a 20 litre day pack but you think it’s too small then you will want something larger, 30 or 35 litres.

This is especially important with backpacking rucksacks, put your gear into an existing pack in order to gauge how big your next pack needs to be – remember to allow for food, fuel and water.

Under 20 Litres

These packs will most likely be for runners and will therefore need to be very stable while they are being worn. Because they are small they often don’t have hip belts because they would sit too high, above the hips – but they do usually have a webbing strap to provide stability. Smaller capacity packs in this category fit like a jerkin and are called Vest packs – these are very stable. Feature wise you should look for accessible pockets and the method of carrying water and gels.

20 - 35 Litres

A Daypack will normally have a padded back and it will usually be stiffened – this gives the rucksack shape and makes sure the load is carried comfortably. Look for how the pack deals with hydration – will it take a bladder system, most have a bladder pocket inside with an outlet for the hydration tube – but some have an externally accessed pocket for the bladder making it easier to remove and refill. Other packs have bottle pockets for drinks bottles, and some packs come with bottles already fitted.

Some people will use 20-35 litre packs for backpacking or adventure racing, if this is the case look for the features that matter for this activity – around the harness system for example – even an ultralight backpacking load will be heavy enough to warrant carrying on the hips rather than the shoulders – so look for a good hipbelt and an internal frame if you are using such a pack for ultralight backpacking.

35-60 Litres

These packs will usually be used for backpacking and that demands that the load is carried on the hips, so an internal frame is essential, one that transfers the load to a decent hipbelt. Supporting the load on the hips makes it easier to carry because the weight is close to your centre of gravity and it minimises the pressure on your shoulders, which are much weaker and will ache much more quickly if loaded up.

Bigger packs will either come in different sizes or have an adjustable back system that allows you to set the ‘back length’ to match your particular back. Be wary of adjustable back systems as they often add to the overall weight of the pack, once you set the length you never have to change it – for the life of the rucksack you are carrying the ‘dead’ weight of the adjustment system. Some recent adjustable back systems achieve the adjustment without adding much weight overall – these are the ones to look for. Buying a ‘fixed back length’ rucksack requires that you know what size you are, you can find this out using the universally recognised method. Follow this LINK.

‘Fit’ of the rucksack is very important and as an online retailer we know that you may have to try a few out before making a final choice. If you buy a rucksack from us spend some time when you receive it making sure it fits comfortably – taking care to keep it in pristine condition load it up in the house and climb the stairs with it – if it’s not right return it and choose another one.

Having determined the capacity and ‘fit’ of the rucksack you can move onto features. For backpacking rucksacks it’s important that the overall weight of the pack is low, without compromising the comfort. A 60 litre backpacking rucksack can weigh anything from 900 grams to 3kg, under 1.5kg is good but the lighter the better consistent with that comfortable harness. Backpacking rucksacks at the lighter end of the spectrum usually have fewer features, though for backpacking we always recommend hipbelt pockets and large stretch mesh pockets on the sides of the pack and the front – this allows you to keep the gear handy that you need without having to continually get inside the pack.

There’s much debate about lids – these help protect the opening from water entry and always have pockets that can keep you organised. But some of the lighter packs don’t have them – preferring rolltop closures to ensure water doesn’t get in the top – leaving out the lid can save up to 15% of the pack weight and apart from a few extra pockets does not add much – which side of the argument you favour is down to personal preference. Another popular feature of a backpacking rucksack is separate compartments – our view is that these certainly add weight but don’t add any versatility to the pack – we think they should be avoided.

Finally a word about fabrics – the heavier packs are truly tough beasts and are over engineered for most users, at the other end of the scale lightweight packs will be made of less durable fabrics and need a bit more care in use. We think this is a small price to pay for having less to carry and we think you’ll agree at the end of a long tough day.

60+ Litres

Some people will carry 60+ litre packs for backpacking, we think that anyone practicing lightweight techniques, and for most 3 season backpacking adventures then 60 Litres should be the limit. Exceptions to this come in when there is a need to carry lots of food and/or water, both of which take up a lot of space and add a lot of weight to your pack.

Another exception may be if you are making an assault on a high mountain, perhaps this requires ropework or you need other protective equipment that adds volume and weight to your gear. Perhaps you are heading to a particularly cold climate and your sleeping bag and clothing takeup a lot more space – or you are backpacking in winter.

If any of these describe your trip then you are probably thinking about a high capacity rucksack. If you need this high capacity then the weight you will be carrying will be similarly quite high. It is particularly important to get a good harness that will allow you to carry the load on your hips – this is the most important thing.

Further advice?