Wrong-sized harnesses are one of the most common pet product returns — and one of the most preventable. A harness that's too loose lets your dog slip out mid-walk. One that's too tight causes chafing, restricts breathing, and makes your dog reluctant to wear it.

The good news: measuring your dog for a harness takes about 60 seconds and requires nothing more than a fabric tape measure. Here's exactly how to do it.

The Two Measurements That Matter

Most harness sizing is based on two measurements: chest girth and neck girth. Of the two, chest girth is by far the more important — it's the measurement most harnesses are primarily sized by, and it's where fit problems usually originate.

Chest Girth (Most Important)

This is the circumference of the widest part of your dog's ribcage — usually just behind the front legs.

How to measure:

1. Stand your dog on a flat surface
2. Find the widest point of their chest (roughly where their front legs meet their body)
3. Wrap the tape measure around the full circumference at that point
4. Pull it snug but not tight — you should be able to slip two fingers underneath
5. Note the measurement in centimetres

Pro tip: If your dog is wriggly, do this right after a walk when they're calmer.

Neck Girth (Secondary)

This is the circumference of your dog's neck where the harness collar sits — typically at the base of the neck, not the throat.

Back Length (For Jacket-Style Harnesses)

Some harnesses — particularly tactical or vest-style ones — also use back length. Measure from the base of the neck (where the collar sits) to the base of the tail.

Harness Size Charts by Breed

The Two-Finger Rule

Regardless of what size you order, always apply the two-finger rule when fitting: slide two fingers under any strap. If you can't fit two fingers, it's too tight. If you can fit a whole hand, it's too loose. This applies to chest straps, belly straps, and neck openings separately.

Common Fitting Problems (and How to Fix Them)

The harness spins sideways: Usually means the belly strap is too loose. Tighten the belly band first, then readjust the chest strap.

Your dog keeps slipping out the front: The neck opening is too large. If your harness has an adjustable neck strap, tighten it. If not, you need a smaller size.

Chafing under the armpits: The belly strap is rubbing in the wrong position. It should sit just behind the front legs, not on them.

Dog actively resists being harnessed: Usually a negative association from past tight fitting. Do several short positive sessions where you touch the harness, feed a treat, put it on briefly, feed more treats. Most dogs come around within a week.

Front-Clip vs Back-Clip: Which Should You Choose?

Back-clip harness: Leash attaches at the back between the shoulder blades. Best for calm walkers and small breeds. Can actually encourage pulling in strong dogs.

Front-clip harness: Leash attaches at the chest. Best for pullers — clips at the chest redirect the dog sideways when they surge forward, breaking the pulling motion naturally.

Dual-clip harness: Has both front and back rings. Most versatile option for everyday use. Our Adjustable No-Pull Tactical Harness has both front and back D-rings, padded chest panel, and full size chart from S to XL.

What If Your Dog Is Between Sizes?

If your dog's chest measurement falls between two sizes: deep-chested breeds (French Bulldog, Boxer, Rottweiler) — size up. Narrow-chested breeds (Greyhound, Whippet, Collie) — size down.

Measuring Puppies

Puppies grow fast. If your puppy is under 6 months, buy a harness with the widest adjustment range possible. Measure every 4–6 weeks during peak growth stages.

Ready to find the right harness? Browse our full range at petivoo.store with free shipping on qualifying orders and 30-day returns if the fit isn't right.