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Trail terms

Big three

Also called big 3

What is the big three in backpacking?

The big three are a backpacker's shelter, sleep system and pack: the three items where most of a kit's weight sits and, as REI puts it, where you can cut the most. The usual advice is to lighten the shelter and sleep system first and choose the pack last.

Big three at a glance

The three
Shelter, sleep system, pack
Ultralight shelter
Under 2 lb solo, 3 lb for two
REI's targets
Ultralight bag or quilt
Under 2 lb
Ultralight pack
Under 2 lb

Why do the big three matter so much?

Because that is where the weight is. A shelter, a sleeping bag or quilt with its pad, and the pack that carries them are the bulkiest things you own, and REI's ultralight guide calls them the items where you can cut the most weight. Shelter is generally the heaviest of the three and likely the most expensive.

Everything else in a kit is a long tail of small items. Trimming those saves ounces; replacing one of the big three can save pounds, which is why every serious attempt to lighten a pack starts here.

What should each of the big three weigh?

REI's ultralight targets are a solo shelter under two pounds, or under three pounds for two people, a sleeping bag or quilt under two pounds, and a pack under two pounds. Hit those and an ultralight base weight, which REI puts at under 10 pounds, becomes realistic.

They are targets for ultralight backpacking, not requirements for backpacking at all. REI puts a traditional backpacker's base weight under 30 pounds and a lightweight one under 20, and replacing even one of the three moves you a long way down that scale.

Why choose the pack last?

Because the pack's size depends on everything else. REI's advice is that of the big three, your pack should be the last thing you consider: lighten the shelter and sleep system first, then pick a pack to carry what you actually ended up with.

Buying the pack first locks in a volume and a load rating before you know what has to fit inside. A lighter, more compact shelter and sleeping bag often mean a smaller pack will do, and REI puts typical ultralight packs at about 30 to 60 liters depending on trip length and gear.

What this means when you're choosing

  • The heaviest of your three first, which for most people is the shelter
  • Your real weights on a scale, not the figures from product listings
  • The sleeping pad counted as part of the sleep system, along with the bag or quilt
  • A pack chosen after the other two, sized to the pile they actually make

The common mistake

Buying the pack first

It is the most visible piece of gear and the one people shop for first, and it is the one that should come last. A pack bought before the shelter and sleep system is sized for gear you have not chosen yet, and it usually ends up bigger and heavier than the kit needs.

Common questions

What are the big three in backpacking?

Your shelter, your sleep system and your pack. The sleep system means the sleeping bag or quilt together with the pad. They are grouped because they are where most of a kit's weight sits.

Which of the big three should you buy first?

The shelter and sleep system, with the pack last. The pack has to fit what the other two add up to, so choosing it first means guessing at a size before you know it.

Where this is defined

Where this comes up

Guides on Tom's Hiking where big three changes which product is right for you.

More in trail terms

Base weight

Base weight is everything in your pack except food, water and fuel: the gear that doesn't get used up. It's the number backpackers compare, because consumables vary with trip length while base weight is a property of your kit.

Ultralight

Ultralight is a style of backpacking built around a base weight under 10 lb. It gets there by making the big three lighter and by carrying fewer things, which trades comfort in camp and margin in bad conditions for comfort while walking.

Fastpacking

Fastpacking is covering a multi-day route with a pack light enough to run in, somewhere between trail running and ultralight backpacking. Typical loads run 8 to 20 liters, and the trip is usually run downhill and on the flat and hiked uphill.

Thru-hiking

Thru-hiking is walking a long trail end to end in one continuous trip, usually within a single season. The Appalachian Trail, Pacific Crest Trail and Continental Divide Trail are the best-known examples in the US, each taking several months.

Shoulder season

The shoulder seasons are spring and autumn, the months either side of settled summer conditions. Days can be warm and nights near freezing, weather changes faster, and gear that works in July is often not enough in late September.

Three-season

Three-season gear is built for spring, summer and autumn but not sustained winter conditions. It's the default rating for most backpacking equipment, and in practice it means handling rain, wind and light frost but not deep snow.

Layering system

A layering system is the practice of combining a moisture-moving base layer, an insulating mid layer and a protective shell, so you can regulate temperature by adding and removing pieces rather than relying on one heavy garment.

Zero day

A zero day is a day on a long trail where you walk no trail miles at all, usually taken in a town to rest, resupply and deal with logistics. A nero is a near-zero: a handful of miles into or out of town with the rest of the day off.

Cowboy camping

Cowboy camping is sleeping outside with no shelter over you: a pad, a bag or quilt, and the sky. It saves the weight and the time of pitching a tent, and it trades away protection from rain, wind, dew, insects and anything that walks past in the night.

Postholing

Postholing is breaking through soft snow with each step and sinking to your shin, knee or thigh, leaving a line of holes behind you. It is exhausting, it can drop your pace to under a mile an hour, and it damages the trail for everyone following.

Slickrock

Slickrock is bare, exposed sandstone with no soil on it and no tread cut into it. You walk on the rock itself and follow cairns rather than a path. Dry sandstone gives excellent grip; wet or dusty sandstone gives very little, which is where the name misleads people.

Trailhead

A trailhead is the designated access point where a trail begins, and usually where you park and start walking. Many have a map board, signs or a toilet. The US Forest Service draws a firm line: a plain junction of two trails, or of a trail and a road, is not a trailhead.

Treeline

Treeline is the elevation, or latitude, above which trees can no longer grow. It is less a line than a zone where trees shrink into stunted, wind-shaped growth, and it sits at very different heights: between 5,000 and 6,000 feet in Washington's Olympics, and above 10,000 in the Sierra.

Backcountry

Backcountry is undeveloped land away from roads and drive-in campgrounds, reached on foot or by water. In US parks it is the opposite of frontcountry, where you drive to a campground, and camping there often needs a permit. It is not the same as legally designated Wilderness.

Section hiking

Section hiking is completing a long trail in pieces, one stretch at a time over separate trips, rather than in one continuous push. The Appalachian Trail Conservancy counts anyone who finishes the whole trail in more than 12 months as a section hiker, and recognizes them as 2,000-milers alongside thru-hikers.

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