Measuring a Cat or Small Dog for a Harness

More harnesses are returned than any other item in a pet shop, and nearly all of them for the same reason: the size was chosen from a weight range on a chart rather than from a measurement of the animal. Weight is a poor proxy for chest circumference. A stocky nine-pound cat and a lean nine-pound cat are different shapes, and only one of them will fit the harness the chart recommends.

The measurement that matters

Girth — the circumference of the chest at its widest point, just behind the front legs. That single number decides whether a harness fits, and every reputable manufacturer publishes a girth range rather than only a weight.

Measure with a soft tape, snug against the coat but not compressing it. If you only have a rigid tape, use a length of string and measure the string afterwards. Take the measurement with the animal standing, not sitting or lying, because the chest changes shape considerably.

The second measurement

Neck circumference matters for harnesses with an over-the-head design and for collars. Measure where the collar naturally sits, low on the neck rather than high under the jaw.

For step-in harnesses, neck size matters less; for over-the-head styles, an animal with a broad head and a narrow neck — many cats, and several dog breeds — can be difficult to fit, and a step-in or fully adjustable design solves it.

The two-finger rule

A correctly fitted harness allows two fingers flat between the strap and the animal at every point. More than that and it can be backed out of; less and it restricts movement and rubs.

Check every strap, not one. It is common for the chest strap to be right and the girth strap loose, and the girth strap is the one that prevents escape.

Sitting between two sizes

Take the larger, and tighten the adjusters. A harness at the top of its adjustment range on a small animal has almost no margin — for winter coat, for a growing puppy or kitten, or simply for a measurement that was a little optimistic.

The exception is a harness with a very short adjustment range, where the larger size may not tighten enough to be secure. Where a manufacturer publishes the adjustment range as well as the size, it is on our product page.

Cats are a special case

Cats escape harnesses that dogs could not, because they can compress their shoulders and reverse out of anything with slack. For cats, a vest-style harness with a wide chest panel is far more secure than a strap harness, and the two-finger rule should be closer to one finger snug.

Introduce it indoors over several days before ever attaching a lead. A cat that has worn a harness for ten minutes and then been taken outside is a cat that will spend the whole time trying to get out of it.

Coat length and season

A long-coated animal measured in winter will measure differently in summer, and by more than people expect — an inch of coat around the chest is two inches of girth. Measure against the body where you can, parting the coat if necessary, and expect a slightly loose fit after a summer clip.

Growing animals

Puppies and kittens outgrow harnesses quickly, and a harness that is too tight causes more harm than one that is slightly loose. Re-measure monthly during the first year, and expect to buy at least twice.

Buying a large harness to grow into is a false economy: an animal that can back out of a harness on a street is a serious problem now, not a saving later.

Signs the fit is wrong

• Rubbing or thinning coat under the front legs — the girth strap is too tight or too far forward.
• The animal walks stiffly or with a shortened front stride — the chest panel is restricting the shoulder.
• The harness rotates during a walk — it is too loose, or the wrong shape for the chest.
• The animal can back out — girth strap loose, or a strap design on an animal that needs a vest.

Before you order

Have two numbers written down: girth at the widest point, and neck. Check both against the manufacturer’s published range on the product page rather than against a weight. If the animal is between sizes, take the larger and use the adjusters.

Girth ranges and adjustment ranges are listed for every harness in collars and walking. If a range is not published by the manufacturer, we say so rather than estimating one.

Introducing a harness properly

A correctly sized harness that the animal hates is no more useful than a badly sized one. Introduce it indoors: leave it on the floor for a day, then put it on for a minute with a treat, then five minutes, then during a meal. Only attach a lead once wearing it is unremarkable.

Cats need considerably longer than dogs — often two weeks rather than two days. A cat that freezes and refuses to walk when a harness goes on is not being difficult; it is a normal first response, and it passes with repetition.

Checking the fit again after a month

Straps loosen, buckles slip and coats change. Re-check the two-finger test monthly, and always after a groom or a seasonal moult, when an animal can be a full size smaller than it was.

The most common late failure is a girth strap that has crept looser over weeks of walking, which nobody notices until the animal backs out of it at a junction. Sixty seconds a month prevents it.