Dog harness: how to choose the right size

Too big, and your dog slips out of the harness the first time a cat walks by. Too small, and it rubs under the legs. The good news: finding the right size takes five minutes and a tape measure. Here’s how to measure your dog, read a size guide and adjust the harness properly.

Harness or collar: why a harness?

A harness spreads the pull across the chest and shoulders rather than the neck. It’s often more comfortable for a dog who pulls on the lead, for a small dog with a delicate neck, or for a dog who doesn’t get on with a collar. A handle on the back, when there is one, also lets you keep your dog close in one move, to cross the road or pass another dog.

A collar is still useful for carrying an ID tag. Many owners keep both: the collar all the time, the harness for walks.

Step 1: measure the chest girth

This is the measurement that matters when choosing a harness size. Weight is only a guide.

Get your dog to stand up straight.
Wrap a soft tape measure just behind the front legs, around the widest part of the rib cage.
Pull it just tight enough to touch the fur, without squeezing.
Write down the measurement in centimetres. Do it once more to check.

No tape measure? A piece of string works: mark where it meets, then lay it flat and measure it with a ruler.

What about the neck?

Some harnesses also ask for the neck girth, measured at the base of the neck, where a collar would sit. On a harness with several adjustment points, it’s mainly the chest girth that sets the size.

Step 2: read the size guide

Every brand has its own guide: a size M from one brand isn’t a size M from another. Always look at the centimetres, not the letter.

For example, for our adjustable reflective harness:

S: chest girth 43 to 56 cm (about 4 to 7 kg)
M: 56 to 69 cm (about 7 to 16 kg)
L: 69 to 81 cm (about 16 to 30 kg)
XL: 81 to 107 cm (about 30 to 50 kg)

Between two sizes?

Go for the larger one and tighten the straps. A harness that’s too small can’t be let out; one that’s a little big can be tightened.

A growing puppy

Puppies grow fast: choose a size where the straps aren’t already at their maximum, and check the fit every two or three weeks.

Step 3: adjust the harness properly

The two-finger rule: you should be able to slide two flat fingers under each strap. Less, and it’s too tight; much more, and your dog may wriggle out.
Nothing in the armpits: the straps shouldn’t rub behind the front legs when your dog walks.
The reverse test: at home, gently pull the lead forward while your dog backs up. If the harness slides over their head, tighten it.
Check again after a few minutes: straps settle a little once in place.

For the first few days, let your dog wear the harness for a few minutes at home, with a treat, before the first real walk. They’ll link it with something nice.

Signs of a poorly fitted harness

Redness or worn fur under the legs or on the chest.
A dog who scratches, limps or refuses to move forward.
A harness that twists to one side when your dog pulls.
A dog who can back out of the harness.

If so, readjust it or change size. And if you notice an injury, show it to your vet.

Choosing the right lead to go with it

Choose the lead according to your dog’s size and where you walk. Our reflective rope lead, for example, comes in three thicknesses:

0.8 cm for small dogs and puppies;
1.0 cm for medium dogs;
1.2 cm for large dogs.

As for length: 120 or 150 cm in town, to keep your dog close; 200 or 300 cm somewhere quiet, to let them explore. Always clip the lead to the ring provided, never to the harness handle.

See and be seen

In autumn and winter, it gets dark early. Reflective strips or threads bounce back headlight beams and help drivers spot your dog. That doesn’t replace caution: by the roadside, keep your dog on the pavement side, on a short lead.

And for long outings, think about water: a water bottle with a built-in bowl slips into a bag and works with one hand.

Find all our walking gear in the Walks section.

Frequently asked questions

My dog weighs 8 kg, should I get S or M?

Go by chest girth rather than weight: two 8 kg dogs can have very different builds. Measure your dog, then choose the size that matches in centimetres.

Can my dog wear the harness all day?

It’s best to take it off at home. A harness worn all the time can rub and catch on things. Keep it for outings.

Does a harness stop a dog from pulling?

A harness makes pulling more comfortable, but it doesn’t teach loose-lead walking. For that, training is key: reward your dog when the lead is slack, and don’t hesitate to ask a dog trainer for advice.