how to choose between a 30l and 45l rucksack for multi-day UK ridge walks

Choosing between a 30L and a 45L rucksack for multi-day ridge walks in the UK is one of those decisions that seems small until you're halfway up a wet, windy fell with your toes numb and your waterproof buried somewhere at the bottom of your pack. Over years of walking ridgelines from the Lake District to the Scottish Highlands I’ve carried both sizes extensively. In this piece I’ll walk you through the practical differences, how I think about packing and weight, and the trade-offs that make one size right for a given walk — and person.

What the numbers actually mean

When manufacturers say 30L or 45L they’re talking about internal volume. That number includes main compartments and often external pockets but not always attachments like hip-belt pockets or sleeping mat straps. In practice, a 30L will comfortably carry a day-to-day kit plus a little food and a lightweight rain layer; a 45L lets you carry more clothing, a stove and fuel, or a bulkier camera setup without cramming.

Typical kit fits I use

To make this concrete, here are two example packs I’ve laid out for UK ridge circuits. These aren’t exhaustive lists but they reflect how I usually pack.

• 30L build (light & fast, 1–2 nights if wildcamping minimal): lightweight bivvy (e.g. Snugpak Stratosphere bivvy), 200–300g sleeping bag/quilt, single pot stove, 1–2 changes of base layers, thin puffy (e.g. Montane or Rab) tucked in, compact waterproof, 1–2 days of food, camera body + one lens (mirrorless), map & compass, first-aid, water bottle (1L), headtorch.
• 45L build (comfort & kit for 2–4 nights or variable weather): small 3-season tent or larger bivvy + tarp, 3-season sleeping bag, stove + fuel, full cook kit, extra clothes (dry kit for evenings), extra layers (thicker puffy), additional camera lenses/kit, large camera tripod or carbon monopod, larger water capacity or purifier, more food, repair kit, battery bank, and optional drone or extra footwear.

Why I sometimes choose 30L

I choose a 30L when the objective is speed, minimalism and moves on rough ground. There’s a freedom to being compact: you’re less tempted to carry “just in case” extras, you can move more nimbly over narrow ridges, and your pack sits higher and closer to your back which improves balance on scrambly sections.

For a good 30L rucksack I often reach for options that have a tidy external pocket system and a supportive hipbelt — examples include the Osprey Talon 33 (a bit over 30L but same idea) or lighter options from Montane and Rab aimed at fastpacking. Key for me is a comfortable suspension and easy access to maps and waterproofs.

Why I sometimes choose 45L

A 45L becomes my go-to when weather is unpredictable, when I’m carrying more camera equipment, or when I expect to need comfort items in the evening (dry clothes, more substantial sleeping bag). For ridge walking in the UK where weather can flip quickly, having the space for a spare warm layer and a reliable shelter lets me stay out longer and recover better in the evening.

My favourite 45L packs for UK ridge routes offer compression straps and a decent hipbelt — think Osprey Atmos/Exos 45 or Lowe Alpine Aeon. The ability to carry a small tent and full cooking kit without cramming is the main draw.

Key questions to decide which works for you

• How long is the trip? One night, and you can probably manage a 30L. Two nights? 45L is often more comfortable unless you’re ultralight.
• How variable will the weather be? In the UK, rain and wind are almost guaranteed. If you want spare dry clothes and a more substantial sleeping bag, lean towards 45L.
• Do you carry a lot of camera kit? If photography is a priority, count lenses, tripod and batteries. Camera gear adds volume quickly — 45L or a dedicated camera insert is often necessary.
• Are you comfortable with ultralight gear? If you’ve invested in lightweight shelter and cookware, you can compress a multi-day kit into 30L. If not, 45L provides a margin for heavier items.
• How important is mobility? If you’re moving fast over narrow ridges and technical ground, a 30L helps with balance and agility.

Packing tips to make each size work

• Use stuff sacks: Compressible dry bags keep gear organised and reduce dead space. I carry a small 2L for essentials and a 10L for sleeping kit.
• Wear heavier items: If you have a bulky jacket or a heavier camera, wear it rather than pack it when moving across exposed ground.
• External carry thoughtfully: Use compression straps for tripods or mats; keep weight close to your back to maintain balance.
• Layer food smartly: Freeze-dried meals compress well and take less room than tins. Carry snacks in soft pouches to save space.

Weight targets I use

These are broad ranges. “Base weight” is my gear weight excluding consumables. On steep, technical ridges I try to keep fully-loaded weight under 8–9 kg for comfort.

Common pitfalls

• Overpacking a 45L: The temptation to fill available space with non-essentials is real. Be deliberate — more volume shouldn’t mean more weight without purpose.
• Underestimating weather: A 30L can feel luxurious on a calm day but miserable if you can’t fit a waterproof and spare warm layer.
• Poor pack fit: Even a well-sized pack is miserable if the hipbelt doesn’t sit on your pelvis or the straps chafe. Fit matters as much as volume.

My personal rule-of-thumb

For single-day ridge traverses or lightweight, one-night plans where I’m prioritising speed and photography with only a single lens, I reach for a 30–33L. For anything more than one night, or where I expect prolonged poor weather or heavier camera gear, I take a 45L. The extra room gives me flexibility to carry a proper shelter, change of clothes, and a second battery without feeling cramped.

In the end, the “right” choice balances what you value on the ridge: speed and agility, or flexibility and comfort. Test both on local routes, note how much you actually use, and tailor your kit — a well-packed 30L can beat a badly-packed 45L any day on a narrow, wild ridge.