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Quick answer
An adult Shih Tzu usually measures 30–45 cm1 around the chest and weighs 4.5–8 kg2.
These are the sizes most adult Shih Tzus need. Your dog may differ, so measure to be sure.
Get an exact size for your dogHow a Shih Tzu is built, and why it matters for fit
The UK breed standard gives a weight of 4.5–8 kg, ideally 4.5–7.5 kg, and a height of not more than 27 cm2. PupClub Couture puts the typical chest at 30–45 cm, and notes that a Shih Tzu in full coat can measure 5–8 cm more than its actual body1.
Shih Tzus are brachycephalic (flat-faced)1. The RSPCA advises walking flat-faced dogs on a harness rather than a collar, to avoid pressure on the neck and help them breathe more easily3.
How to measure your Shih Tzu, step by step
- Get a soft tape measure, or a piece of string and a ruler. Stand your dog on a level floor with all four feet square underneath it.
- Find the measuring point: the widest part of the ribcage, just behind the front legs4. Julius-K9 asks you to measure a set distance behind the front legs, which depends on the size: two finger-widths for the Baby sizes, three for Mini-Mini and Mini, and four for size 0 and up5.
- Wrap the tape all the way round. Keep it flat and untwisted, snug against the body but not squeezing. Read the number in centimetres where the end meets the tape.
- Measure twice4. If the two readings differ, use the larger one.
- Weigh your dog too. Julius-K9 gives a weight range for every size as a second guide5; the other brands here size by chest only.
Shih Tzu measuring tips
- Press the tape gently through the coat so you measure the body, not the fluff1.
- Measure again after every groom and adjust the harness. A clipped coat means a looser fit.
- Keep the neck strap and tape well clear of the throat.
Want every detail, including neck, back length and weighing at home? Read our complete guide to measuring your dog.
Shih Tzu harness size by brand
Each brand cuts its sizes differently, so the same dog can be a different size, or a different letter, in each. Here is how a typical adult Shih Tzu fits each chart, and why.
Julius-K9
IDC Powerharness
Julius-K9 lists a chest range and a weight range for every size5. Chest girth is the main guide; we use weight to choose between two sizes when the chest fits both.
- A smaller Shih Tzu (chest 30 cm, 4.5 kg): size Baby 1
- A typical Shih Tzu (chest 37.5 cm, 6.5 kg): size Baby 2
- A larger Shih Tzu (chest 45 cm, 8 kg): size Mini-Mini (also fits Baby 2)
Overlaps in the Shih Tzu range: 33–36 cm: sizes Baby 1 and Baby 2 both fit; 40–45 cm: sizes Baby 2 and Mini-Mini both fit.
Sizes overlap by design; chest girth is the main guide, weight is secondary.
| Size | Chest | Weight |
|---|---|---|
| Baby 1 | 29–36 cm | 0.8–3 kg |
| Baby 2 | 33–45 cm | 2–5 kg |
| Mini-Mini | 40–53 cm | 4–7 kg |
| Mini | 49–67 cm | 7–15 kg |
| 0 | 58–76 cm | 14–25 kg |
| 1 | 63–85 cm | 23–30 kg |
| 2 | 71–96 cm | 28–40 kg |
| 3 | 82–115 cm | 40–70 kg |
| 4 | 96–138 cm | 70–90 kg |
Highlighted rows are the sizes typical adult Shih Tzus need.
Check price on AmazonRuffwear
Front Range Harness
Ruffwear sizes the Front Range Harness by chest girth only6, so your tape measure is all you need.
- A smaller Shih Tzu (chest 30 cm): outside this chart
- A typical Shih Tzu (chest 37.5 cm): size XXS
- A larger Shih Tzu (chest 45 cm): size XS
Some very small or very large Shih Tzus fall outside this chart.
Sized by chest girth only.
| Size | Chest |
|---|---|
| XXS | 33–43 cm |
| XS | 43–56 cm |
| S | 56–69 cm |
| M | 69–81 cm |
| L/XL | 81–107 cm |
Highlighted rows are the sizes typical adult Shih Tzus need.
Check price on AmazonBailey & Coco
Trail & Glow Harness
Bailey & Coco sizes the Trail & Glow Harness by chest girth only7, so your tape measure is all you need.
- A smaller Shih Tzu (chest 30 cm): size XXS (also fits XS)
- A typical Shih Tzu (chest 37.5 cm): size XS (also fits XXS, S)
- A larger Shih Tzu (chest 45 cm): size S (also fits XS, M)
Overlaps in the Shih Tzu range: 30–41 cm: sizes XXS and XS both fit; 35–45 cm: sizes XS and S both fit; 40–45 cm: sizes S and M both fit.
Very adjustable, so neighbouring sizes overlap a lot. Sized by chest girth only.
| Size | Chest |
|---|---|
| XXS | 22–41 cm |
| XS | 26–50 cm |
| S | 35–66 cm |
| M | 40–71 cm |
| L | 55–83 cm |
| XL | 71–99 cm |
Highlighted rows are the sizes typical adult Shih Tzus need.
Check price on AmazonPuppies and growing dogs: when to re-measure
Small dogs reach adult weight sooner than large breeds8. The coat keeps changing, though, so keep checking the fit.
The largest study of puppy growth so far, based on records from over 6 million young dogs, grouped dogs by adult weight: under 6.5 kg, 6.5–9, 9–15, 15–30 and 30–40 kg8. An adult Shih Tzu at 4.5–8 kg falls in the under 6.5 kg and 6.5–9 kg groups.
Size a puppy on its chest measurement today, not on the size you expect it to reach4. A harness bought to "grow into" is loose now, and a loose harness slips, rubs and is easier to back out of.
While your puppy is growing fast, we suggest measuring its chest every two weeks, then monthly until it stops changing. A quick check in between: if you can no longer slide two fingers under the straps, measure again.
Most harnesses adjust over a good part of their range, so a growing puppy may stay in one size for a while. When your puppy's chest reaches the top of its size's range, move up.
If your Shih Tzu is between two sizes
Brand charts often overlap, so a chest measurement can fall inside two sizes. Here is where that happens for a typical adult Shih Tzu:
- Julius-K9: 33–36 cm: sizes Baby 1 and Baby 2 both fit; 40–45 cm: sizes Baby 2 and Mini-Mini both fit.
- Ruffwear: no overlapping sizes in this range.
- Bailey & Coco: 30–41 cm: sizes XXS and XS both fit; 35–45 cm: sizes XS and S both fit; 40–45 cm: sizes S and M both fit.
How to choose:
- Our size finder picks the size where your dog's measurement sits nearer the middle of the range, so the harness can be adjusted either way.
- Ruffwear says that if your dog is right on the border between two sizes and fully grown, choose the larger size6. For a growing puppy that is truly between sizes, Ruffwear also suggests the larger one4.
- For Julius-K9, check the weight ranges too: if your dog's weight only fits one of the two sizes, go with that one5.
- Deep-chested dogs with a narrow waist can slip a loose harness, so if the larger size would only just fit on its tightest setting, the smaller one is usually safer.
Fit checks when the harness arrives
Two-finger rule
You should be able to slide two fingers flat under every strap, and no more6. Tighter than that can rub; looser can slip.
Strap behind the front legs
The strap around the body should sit a little way behind the front legs, not pressed up into the "armpit", where it will rub as your dog walks.
Nothing on the throat
Every strap at the front should sit on the breastbone or low on the chest, not across the throat.
Free shoulders
Watch your dog walk and trot. Its stride should look the same as without the harness. A small study found harnesses can shorten how far the shoulder reaches forward9, so if the stride looks shorter, adjust the fit or try another style.
Check for rubbing
After the first few walks, look behind the front legs, under the chest and around the neck for redness or broken hairs. If you find any, loosen or reposition the harness. If the skin is sore, stop using it and ask your vet.
Escape test
With the harness on, gently pull the lead forwards, then backwards and upwards. The harness shouldn't slide over the shoulders or ribs. If it does, tighten it, or choose a design with an extra strap behind the ribcage.
Re-check after a week
Webbing and buckles can settle in the first few walks. Check the two-finger fit again after a week.
Harness styles that suit a Shih Tzu
Step-in harness
Easy to put on without pulling anything over the head or face.
Y-front harness that sits low on the chest
Keeps every strap away from the throat, which matters for a flat-faced dog.
Lightweight, breathable materials
Flat-faced dogs can struggle in the heat3, so avoid thick padded vests on warm days.
Be careful with
- Any strap that crosses the front of the throat.
- Thick vest harnesses in warm weather.
Common mistakes
- Measuring over a full coat, which can add 5–8 cm1.
- Walking a Shih Tzu on a collar and lead instead of a harness. The RSPCA recommends a harness for flat-faced dogs3.
- Measuring the neck instead of the chest. Harness sizes are set by chest girth.
- Assuming a size letter means the same thing in every brand. A Medium in one brand can be a Large in another, so check each chart in centimetres.
- Buying a size up "to grow into" for a puppy.
A note on health
If your Shih Tzu breathes noisily or struggles on walks, talk to your vet. A harness keeps pressure off the neck, but it doesn't treat breathing problems.
Collar and ID tag: the UK rule
In the UK, a harness doesn't replace a collar. A dog in a public place must wear a collar with the owner's name and address on it, or on a tag or plate attached to it10. Many owners clip the lead to the harness and use the collar for ID.
Shih Tzu harness questions
What size harness does a Shih Tzu need?
An adult Shih Tzu usually has a chest of 30–45 cm and weighs 4.5–8 kg2. That usually means Julius-K9 IDC Powerharness: sizes Baby 1 to Mini-Mini; Ruffwear Front Range Harness: sizes XXS or XS; Bailey & Coco Trail & Glow Harness: sizes XXS to S. Measure your dog's chest to get the exact size.
How do I measure my Shih Tzu for a harness?
Stand your dog square, then wrap a soft tape around the widest part of the chest just behind the front legs4. Keep it flat and snug and read it in centimetres. Measure twice. See our full guide to measuring your dog.
What size harness for a Shih Tzu puppy?
Size a puppy on its chest measurement today, not its expected adult size4. Measure every couple of weeks while it grows fast and move up a size when its chest reaches the top of the current size.
What if my Shih Tzu is between two harness sizes?
Should a Shih Tzu wear a harness or a collar?
Why does my Shih Tzu's harness fit differently after grooming?
Because a full coat can add 5–8 cm to the chest measurement1. Re-adjust to the two-finger fit after each groom.
Is a Shih Tzu an XS or S harness?
It depends on the brand and the dog. Compare your dog's chest in centimetres with each chart, or use the size finder.