Hiking Backpack Size Guide: What Size You Actually Need

Last updated: April 2026 — carried, compared, and still adjusting.

The wrong backpack size is the fastest way to turn a hike into a grind. Too small and you end up lashing a sleeping bag to the outside, watching it catch on every low branch. Too big and you'll pack more than you need, because the space is there, and your knees will find out about it on the descent. The rule sounds simple — day hikes 15 to 25 litres, weekend trips 28 to 45, multi-day treks 50 and up — but litres are only half the equation. Torso length and hip-belt fit decide whether those same litres sit on your shoulders or on your hips, and that's the difference between a sack you carry and a pack that carries itself.

This guide is what I tell friends who are about to buy their first real pack. You'll find a quick decision table, a picks-by-usage list with volumes vetted in stock, a section on torso measurement (because it matters more than you think), notes on women's and shorter-torso fits, and an honest line on what we don't sell. Skip to the section you need — the clickable table of contents above is the fastest route.

The Quick Answer: What Size for What Hike

If you only read one section, this is it. The numbers are ranges because the right volume depends on your gear, the season, and whether you carry a stove or not.

Trip type	Duration	Volume	Typical load	Featured pick
Day hike (fast & light)	Under 6h, no camp	15–20L	3–5 kg	Millet Mixt 15
Day hike (all-round)	Full day, layers & lunch	22–28L	5–8 kg	Patagonia Black Hole 25L
Overnight / weekend	1–3 nights, shelter	30–45L	8–12 kg	Patagonia Refugio 32L
Multi-day trek	3–7 nights, self-supported	50–65L	12–18 kg	Deuter Access 55
Thru-hike / expedition	7+ nights, cold-weather	65–80L	15–22 kg	See note on what we don't stock

Our Picks by Usage (2026)

Everything below is in stock as of publication, brand-mixed on purpose — a curator's bench, not a sales page. If a pack fits the job and the wearer, it earns the spot.

Day hikes — 15 to 25 litres

• Millet Mixt 15 — 15L, 320 g. The stripped-down choice for summit pushes and fast ridges. Alpine DNA, minimal frame, a pack you forget you're wearing.
• Patagonia Black Hole 25L — 25L in recycled TPU-laminated ripstop. The all-rounder. Carries a day's layers, a DSLR, a thermos, shrugs off rain, and will outlast three pairs of boots.
• Topo Designs Rover Trail Pack 22L — 22L, recycled nylon, Colorado-built. The hybrid — trail on Saturday, bike-to-work on Monday.
• Patagonia Terravia 22L — 22L, lightweight technical build, ventilated back panel. For hot-weather day hikes where air flow matters as much as volume.

Overnight & weekend — 28 to 45 litres

• Deuter Futura Pro 30 — 30L with Deuter's Aircomfort Sensic frame. The technical weekend pack — proper hip belt, load lifters, airy mesh back. German engineering, honest price.
• Patagonia Refugio 32L — 32L recycled poly, laptop-ready but trail-capable. The crossover pack for people whose weekend starts straight after work.
• Mero Mero Mini Smogen 30L — 30L, recycled fabric, French design. The softer shape — for weekends that lean more Patagonia Stories than military spec.
• Patagonia Terravia 36L — 36L technical pack with proper suspension. Pushes into overnight territory for minimalists.

Multi-day — 50 to 65 litres

• Deuter Access 55 — 55L with Deuter's Aircontact suspension. The only multi-day pack we currently stock, and we stock it because it earns every gram — top-loader with a floating lid, rain cover included, a hip belt you can actually live in for a week.

Day Hikes: 15 to 25 Litres, and Why That's Enough

A day hike is anything you can walk out of before sunset. No shelter, no cookset, no more than a light jacket you might or might not put on. The temptation is to go bigger "just in case" — don't. A 35-litre pack on a four-hour ridge walk is a 35-litre pack you'll fill with snacks and a second fleece you didn't need.

Fifteen to twenty litres is plenty for summer days: water bladder or two bottles, a windbreaker, sandwiches, a first-aid kit, phone, keys, a thin puffy if the forecast is iffy. Twenty-two to twenty-eight is the range for shoulder seasons — colder starts, more layers, maybe a second water bottle, a small thermos, a pair of gloves. If you carry a DSLR or a drone, tack on five litres.

The rule of thumb: pack what you carry, weigh it, and pick a volume that fits it with 10% to spare. Not 30%. You don't need the headroom.

Is 20L enough for a day hike?

For most people, yes. Twenty litres carries three to four kilos of gear without strain, which is roughly a full-day summer load. If you're a parent carrying the family's water, a photographer hauling a second lens, or hiking in winter with a down jacket, bump up to 25 or 28. Otherwise, 20L is the sweet spot.

Is 30L too big for day hikes?

For fast-and-light summer days, yes — 30L will feel bulky on your back and tempt you to pack what you don't need. For full-day hikes in cold weather, with a DSLR or with small kids (more snacks, more everything), 30L is fine. Think of 30L as the crossover volume between day hikes and overnights.

Overnight & Weekend: 28 to 45 Litres

Once you sleep on the trail, everything scales up: a shelter, a sleeping bag, a mat, a stove. Thirty to thirty-five litres works if you're ultralight — silnylon tarp, down quilt, alcohol stove, no change of clothes. Most people aren't ultralight on weekend one, and that's fine; 40 to 45 litres gives you breathing room for a proper tent and a warm layer you'll be glad to have.

The other number that matters at this volume is the hip belt. A 30-litre daypack without a real hip belt will punish your shoulders after four hours. A 35-litre pack with a padded belt and load lifters rides on your hips, which is where heavy loads belong. If you're weighing a weekend pack and it doesn't have load lifters (the straps between the top of the shoulder harness and the top of the pack), walk away.

How many litres for a 3-day hike?

Thirty-five to forty-five litres for three-season use. Add five to ten litres for winter, cooking-heavy trips, or if you pack a bulkier sleep system. The lower end (35L) works if you're sharing a tent and splitting group gear with a partner.

What size backpack for an overnight hike?

Thirty to thirty-five litres is enough for one night in summer if you're tent-sharing and your sleep system packs small. Solo, in a shoulder season, with a warmer quilt, you'll want 35 to 40L without fighting the zipper.

Multi-Day & Thru-Hiking: 50 to 70 Litres (and the Brands We Don't Sell)

Past three or four nights self-supported, or in colder weather with a proper winter sleep system, you cross the fifty-litre line. This is the volume where the pack becomes a suspension system first and a container second — the hip belt, the frame, the load lifters, the back panel are all doing real work, and the wrong pack ruins a week.

We carry one multi-day option: the Deuter Access 55, a 55L top-loader with Deuter's Aircontact suspension, included rain cover, a hip belt you can genuinely live in, and a price that isn't trying to be expensive. It's the pack I've seen most often on long traverses — not because it's the flashiest, but because it does the job and disappears.

That said, we won't pretend we cover the whole thru-hiking market. Here's what we don't stock, and what you should look at if you need it:

• Expedition 65-80L (winter, alpine, 10+ days) — Osprey Aether Plus 70, Gregory Baltoro 75, Arc'teryx Bora 75, Mystery Ranch Terraframe 80. These are the workhorses for serious expedition weight.
• Thru-hiking ultralight (50-65L, weight-obsessed) — Hyperlite Mountain Gear Southwest 55 and 3400, Gossamer Gear Mariposa 60, Pa'lante V2, Zpacks Arc Haul. Dyneema Composite Fabric, ultralight frames, for people who count grams on the Appalachian Trail.
• Technical mountaineering 50-70L — Black Diamond Speed 50, Blue Ice Warthog, Mammut Trion Nordwand. Stripped-down alpine packs, not really trekking packs.

These are excellent. We don't sell them because our curation leans toward brands with a longer-term manufacturing ethos, and because thru-hiking is a specialist space where you should buy from specialists. If you're walking the GR20, the PCT, or the Haute Route, buy from a dedicated expedition shop. If you're doing a four- to seven-day trek with normal gear, the Deuter Access 55 will take care of you.

How many litres for backpacking?

For multi-day backpacking with a three-season setup: 50 to 60 litres. For four-season / winter backpacking with a heavier sleep system, heavier layers, and more food: 65 to 75L. For ultralight thru-hiking with specialised gear: 50 to 55L is plenty.

55L or 65L for multi-day?

Fifty-five if you pack tight and your gear is modern (compressible quilts, small stoves, packable tents). Sixty-five if you're new to multi-day, carry a bulkier sleep system, hike in shoulder-season cold, or are the designated group-gear carrier. When in doubt, err on 55 — a smaller pack enforces tighter packing, and tighter packing weighs less.

Torso Length: The Number That Matters More Than Litres

This is where most people go wrong. They pick a volume, not a fit. And fit — specifically torso length — is what makes a loaded pack ride on your hips instead of on your neck.

Torso length is the distance along your spine from the C7 vertebra (the bony knob at the base of your neck when you tip your head forward) down to the iliac crest (the top of your hip bones, where a hip belt sits). It has almost no correlation with your total height. Two people who are both 175 cm tall can have torsos of 45 cm and 52 cm — that's a size S versus a size L in most brands.

How to measure your torso in 3 minutes

1. Find C7. Stand upright and tip your head forward. The most prominent vertebra at the base of your neck is C7. Mark it with a finger or a post-it.
2. Find the iliac crest. Place your hands on your waist with thumbs pointing backwards, fingers forward. Slide them down until they rest on the tops of your hip bones. Draw an imaginary line between your thumbs across your spine — that's the iliac crest.
3. Measure. Use a flexible tape measure along the curve of your spine from C7 to the iliac crest line. The number in centimetres is your torso length.

Most brands use three categories: short (under 46 cm), regular (46–51 cm), long (over 51 cm). Deuter, Osprey and Gregory publish specific ranges per model. Patagonia tends to run one size per pack with adjustable harnesses. When a pack is available in multiple torso sizes, always pick by torso length, never by height.

Women's Fit & Shorter Torsos

"Women's" packs aren't a marketing gimmick — they're a real set of design adjustments for people with shorter torsos, narrower shoulders, and a different pelvic geometry. The shoulder straps are closer together and shaped around the chest, the hip belt has a steeper angle to sit on a more pronounced iliac crest, and the torso length maxes out lower.

That said, men with short torsos are often best served by a "women's" pack, and women with long torsos sometimes fit a "unisex" size better. Don't treat the label as a rule — treat torso length as the rule.

Deuter labels women's packs with an "SL" suffix (slender, not small). The Deuter Futura Pro 30 SL and Futura Pro 34 SL are the two we'd point to for shorter-torso hikers doing day-to-weekend trips. They're the same pack as the unisex Futura, just re-cut.

The Fit Check: Load It, Walk, Adjust

The only way to know a pack fits is to carry it loaded. If you're buying online, do this the day it arrives — before you cut the tags.

1. Fill it with weight. Use 8 to 12 kg of books or water bottles. An empty pack will fit anything; a loaded pack will tell you the truth.
2. Loosen every strap, then cinch the hip belt first. The hip belt should sit on your iliac crest, not above (digging in) or below (sliding off). Seventy per cent of the load should land on your hips.
3. Tighten the shoulder straps. Snug, not pulling. The shoulder yoke should sit flush against your back.
4. Tension the load lifters to roughly 45°. These pull the top of the pack in toward your back, putting weight on your hips rather than pulling you backwards.
5. Clip the sternum strap. An inch or two below your collarbone, just snug enough to stop the shoulder straps from sliding outward.
6. Walk around for 20 minutes, up and down stairs if possible. Any hot spots, shoulder pinch, or hip-bone rubbing will show up in the first 20 minutes, not the first 20 metres.

If it doesn't fit after adjustment, it doesn't fit. Send it back. A pack that fights your body on lap one of a store will fight it harder on day four of a trek.

Frequently Asked Questions

What size backpack do I need for a day hike?

Fifteen to twenty-five litres, depending on gear and season. Fast-and-light summer days: 15L. All-round summer: 20L. Cold or photography-heavy days: 25L.

What size backpack for backpacking?

Fifty to sixty-five litres for three-season multi-day use. Go smaller (50-55L) if you pack tight with modern ultralight gear, bigger (65-75L) for winter, extended trips, or if you're new to the pack-light mindset.

Is a 40L backpack big enough for a week?

Only if you're an experienced ultralight hiker with dialled-in gear, or if you're resupplying along the way (PCT-style). For a normal week-long trek with standard sleep and cook systems, 55 to 65L is the realistic range.

How big of a backpack do I need for a 3-day hike?

Thirty-five to forty-five litres for three-season, shelter-sharing trips. Solo and in colder conditions, 45 to 55L.

Can a 65L backpack be a carry-on?

No. Most airlines cap carry-ons at 40L or 55 × 35 × 25 cm. A 65L pack has to be checked. If you need a trekking pack that flies as carry-on, look at the 35-40L range.

What size hiking backpack for a petite female?

Look for packs with a torso range starting at 38-42 cm. Deuter SL (slender) models, Osprey WS models, and Gregory Deva/Jade all offer XS fits. Volume-wise, the usage rule still applies — daypack 15-22L, weekend 28-35L, multi-day 50-60L.

What's the difference between a 55L and 65L backpack?

Ten litres of gear room — roughly a bear canister, an extra day of food, or a bulkier sleep system. 55L pushes tight packing; 65L forgives sloppy packing. For most weeklong trips with standard gear, 55L is enough.

Do I need a rain cover on a hiking backpack?

Yes, unless the pack is explicitly waterproof (roll-top with coated fabric and taped seams). Most hiking packs are water-resistant, not waterproof. Check our guide on how to know if a bag is waterproof for the full rundown.

Bottom Line

Volume follows the trip: 15-25L for day hikes, 28-45L for weekends, 50-65L for multi-day, 65L+ for expedition and thru-hiking. But volume is a starting point, not an answer. Torso length, hip-belt fit, and load transfer decide whether those litres feel like cargo or like a part of you. Measure your torso, try the pack loaded, and don't let anyone sell you on size alone.

Browse the full lineup in hiking backpacks or commuter backpacks if the line between hike and commute is blurry. For the weight-obsessed, our sustainable backpack picks lean lighter and built-to-last.