Fit and sizing

Iliac crest

Also called hip shelf, top of the hip bone

What is the iliac crest?

The iliac crest is the curved top edge of your pelvis, the ridge you feel when you put your hands on your hips. It's the shelf a backpack hipbelt sits on, and the lower anchor point for measuring torso length.

What it is: Top edge of the ilium (pelvis)
Role in fit: Hipbelt contact point
Belt position: Padding centered on the crest

How to find it

Put your hands on your hips the way you would while waiting for something. The hard ridge under your palms is the iliac crest. It's the widest part of your pelvis and, structurally, the only place on your body that will happily carry thirty pounds all day.

Where the hipbelt should sit on it

A hipbelt is supposed to wrap that ridge with the padding centered on it, roughly half above and half below. Ride the belt too high and it sits on soft abdomen, which hurts within a mile. Too low and it slides down your thighs and the weight goes back to your shoulders, which is what people describe when they say a pack feels heavier than it should.

Why torso length is measured to it

The crest also anchors the bottom of a torso measurement. That's why the number is neck to hips rather than neck to waist: your waist moves depending on how you're standing and what you ate, and your pelvis doesn't.

What this means when you're choosing

A hipbelt sized separately from the pack's torso size, which good packs offer
Padding that wraps the crest rather than sitting above or below it
An interchangeable belt if you are between sizes

The common mistake

Wearing the belt on your waist

The belt belongs on the bony ridge, roughly half the padding above it and half below. Worn up on the soft waist it has nothing structural to push against, so it slides down under load and takes the weight back to your shoulders.

Common questions

Should the hipbelt sit above or below my iliac crest?

Neither, quite. Center the padded part on the ridge so it grips the flare of your pelvis from both sides. If the whole belt sits above the bone you're squeezing your stomach, and if it sits below you're just wearing a very heavy skirt.

Does hip size change what belt I need?

It changes the belt length, not the position. Most makers sell hipbelts in two or three lengths independently of the pack's torso size, and on some packs the belt is swappable, which is worth knowing if your torso and your waist land in different sizes.

Where this comes up

Guides on Tom's Hiking where iliac crest changes which product is right for you.

More in fit and sizing

Torso length

Torso length is the distance from the bony bump at the base of your neck down to the top of your hip bones. It's the measurement backpack sizes are built around, and it has almost nothing to do with how tall you are.

Last

A last is the foot-shaped mould a shoe or boot is built around. It sets the width, the volume, the shape of the toe box and the heel cup, which is why two pairs in the same size from different brands can fit completely differently.

Toe box

The toe box is the front of a shoe, from roughly the ball of the foot forward. Its width and height decide whether your toes can splay under load, which is what stops black toenails and blisters on long descents.

Surgeon's knot

A surgeon's knot is a lacing trick where you wrap the laces twice instead of once before pulling tight. The extra wrap holds tension in place, letting you lock your heel down while leaving the toe box loose.

Gusseted crotch

A gusseted crotch is an extra diamond or triangle of fabric sewn into hiking pants so four seams do not meet at a single point. It spreads the load of a high step across several seams, which is why gusseted pants do not bind or split at the crotch.

Short liner

A short liner is the brief, boxer or compression layer sewn inside running shorts and worn instead of underwear. Its cut is what decides whether long runs chafe: a brief covers little, a boxer liner reaches the inner thigh, and a 2-in-1 anchors to the shell so it cannot ride up.

Inseam

Inseam is the length of a garment's inner leg seam, measured from the crotch to the hem, and it is how running shorts are sized. Trail shorts run from about three inches to nine, and five to seven covers most trail running.

Chafing

Chafing is skin worn raw by repeated friction, usually where wet fabric rubs skin or skin rubs skin over hours. On a run it starts at the inner thigh, and dried sweat leaves abrasive salt behind that makes it considerably worse.

Last reviewed August 13, 2026. Back to the glossary