What Size Dog Hiking Backpack Do I Need? | Measure Girth, Not Weight

Choosing the right size dog hiking backpack comes down to one measurement: the girth around the widest part of your dog’s ribcage, just behind the front legs. Ruffwear, a leading maker of dog packs, says pack sizing is determined primarily by girth, with back length only helping when a dog falls between sizes. Guessing by breed or weight is the most common mistake—and it leads to packs that slip, chafe, or swing into your dog’s legs mid-hike.

This guide covers how to measure correctly, how to read size charts, and how to check the fit before you ever hit the trail.

Measure Your Dog’s Girth The Right Way

Get your dog standing square on all four paws, relaxed and not hunched. Take a flexible fabric measuring tape and wrap it around the widest point of the ribcage—right behind the front legs. The tape should be snug but not tight enough to compress the fur or skin.

Write that number down in inches and centimeters, then compare it directly against the manufacturer’s size chart for the specific pack you want. Ruffwear’s saddlebag-style hiking packs, like the Approach and Front Range Day Pack, use girth as the primary sizing input.

If your dog’s girth falls right on the boundary between two sizes, use back length as the tiebreaker. Measure from the base of the neck (where the collar sits) to the base of the tail, and choose the size whose back length better matches your dog’s proportions.

Carrier Backpacks Size Differently Than Saddlebags

A carrier-style backpack—the kind designed to hold a small dog inside a compartment—uses back length as the primary measurement, with girth as a secondary check. Measure from the base of the neck to the base of the tail, and confirm the girth fits comfortably inside the carrier’s opening.

Weight caps matter more here. Exceeding a carrier’s weight cap is a safety issue, not just a fit issue—the harness and attachment points are only rated for so much load.

How Much Weight Should A Dog Carry?

Keep the total load—pack plus food, water, and gear—under 25% of your dog’s body weight. For a 45-pound dog, that means no more than 11.25 pounds total.

First-time backpackers should start well below that. A new dog should carry closer to 10–15% of body weight for the first several outings, letting them build conditioning and tolerance gradually. Overloading beyond the dog’s fitness level causes sore muscles, chafing, and a dog that learns to dread the pack.

Fit Check Before You Hike

Once the pack is on and buckled, do a quick test walk around the yard before committing to a trail. The checklist is short but critical:

• The pannier bags should clear the elbows during a normal walk. If they contact the elbows, the pack sits too low and needs cinching up.
• The front edge of each pannier should clear the last rib by a small margin. If it presses against the ribs, the pack is too long for your dog’s proportions.
• The bags should not swing into the rear legs at any point in the stride.
• The chest strap should rest flat on the sternum, not on the shoulders or in the armpits, which restricts movement and causes chafing.

Adjust the straps and re-check. A pack that fits correctly stays put during a trot, distributes weight evenly across the back, and doesn’t shift when the dog stops or turns. If you are weighing options and want to see tested models side by side, our roundup of the best dog hiking backpacks on the market compares fit, capacity, and durability across top brands.

Sizing a dog pack is a two-step job: measure girth for saddlebags or back length for carriers, then check the fit while the dog walks. The 25% body-weight limit is a hard ceiling, not a starting point—begin lighter and build up. A properly fitted pack makes the difference between a dog that trots happily ahead and one that stops dead on the trail.