The Edit — Pets
ThunderShirt: The 80% and 89% Claims Against the Ratings
Thundershirt publishes 2 improvement figures: 80% on its own site and 89% on Amazon. Its 3 most-reviewed sizes rate 4.2 to 4.3 across 77,477 ratings, and owners split more sharply than either figure suggests.
This guide is research-led: we have not handled these units ourselves. If you buy through our links we may earn a commission — it never changes a pick. How we choose
No ThunderShirt was fitted to a dog for this page. This is an evidence profile: the published specification and the maker’s own claims, read against what owners consistently report across 3 size listings on Amazon. The method follows the house rule of highest rating first, then most ratings, which puts the small size ahead of the medium, whose sample is twice as large.
The quick list
Every pick, in order. Jump to the full test on any of them.
- Highest-rated size listing
ThunderShirt for Dogs Calming Anxiety Vest, Small
4.3 across 21,495 ratings, a tenth above the other sizes, with owners describing it as easy to put on.
4.3from 21,495 verified reviews - The deepest evidence base
ThunderShirt for Dogs Calming Anxiety Vest, Medium
4.2 across 43,020 ratings, the most-reviewed calming wrap in Amazon's search results on 16 September 2026, for a 25-inch chest and dogs from 20 lb.
4.2from 43,020 verified reviews - For bigger dogs
ThunderShirt for Dogs Calming Anxiety Vest, Large
4.2 across 12,962 ratings, where the storm reports are strongest and the difficulty of fastening it comes up most.
4.2from 12,962 verified reviews
80% and 89% are owner-reported figures, not trial results
Thundershirt’s product page says 80% of users see improvement in their dog’s anxiety, citing a customer survey. The medium Amazon listing says 89% of pet parents reported improvement in stress-related behaviours, marked with an asterisk.
Both figures come from owners describing their own dogs, and neither page describes a control group. A survey of buyers can overstate a result, because owners who saw no change may be less likely to reply. The figures show that many owners are satisfied. They do not show how much of the calm came from the wrap.
The ratings show a sharper split than either claim
The 3 most-reviewed ThunderShirt size listings together carry 77,477 ratings, at 4.2, 4.2 and 4.3. That is a solid rating, though below the 4.4 to 4.8 range of the top 30 products on Amazon’s Pet Supplies Best Sellers list read the same day.
Owners explain the gap directly. Many describe a dog that stops shaking during storms. A consistent minority describe no change at all, and some say the wrap was hard to fasten on a frightened dog. Owner reports rarely sit in the middle, which fits a product that works well for some dogs and not at all for others.
ThunderShirt for Dogs Calming Anxiety Vest, Medium
4.2 across 43,020 ratings, the most-reviewed calming wrap in Amazon's search results on 16 September 2026, for a 25-inch chest and dogs from 20 lb.
Current price shown on Amazon. We may earn a commission.
| Chest | 25 in |
|---|---|
| Minimum weight | 20 lb |
| Weight of wrap | 8.4 oz |
43,020 ratings is the deepest sample of any calming wrap in the Amazon search results read for this page, and this is the size listing that carries the 89% claim. Owners describe dogs taking to it easily, and several name separation anxiety specifically.
Opinion on whether it works is openly divided, and so is opinion on value. The listing gives a 25-inch chest, a 20 lb minimum weight and a wrap weight of 8.4 oz.
Buy it if
- A mid-sized dog, measured at the chest
- You want the largest sample of owner reports
Don't buy it if
- Your dog will not stand still to be fastened
Sizing by chest girth decides whether pressure is even
A compression wrap works by constant, even pressure, which Thundershirt compares to swaddling an infant. A wrap that is too loose applies none, and one that is too tight is simply uncomfortable. The medium listing, for example, gives a 25-inch chest and a 20 lb minimum weight.
Thundershirt’s sizing uses weight and chest girth, and it advises sizing down when a dog sits at the edge of a weight range. A deep-chested dog can measure into a different size than its weight suggests, so the tape measure should settle it. The same measuring habit applies to a harness, and how a dog harness should fit sets out the checks.
ThunderShirt for Dogs Calming Anxiety Vest, Small
4.3 across 21,495 ratings, a tenth above the other sizes, with owners describing it as easy to put on.
Current price shown on Amazon. We may earn a commission.
| Size | Small |
|---|---|
| Mechanism | Constant torso pressure |
| Evidence | 21,495 ratings |
4.3 across 21,495 ratings makes the small the highest-rated listing, and so it ranks first by the house rule on half the medium’s evidence. Owners call it easy to get on and off and say their dogs relax in it.
Opinion on value is mixed here too. A tenth of a point across 2 samples this size is a small gap, and it is not a reason to choose a size that does not fit.
Buy it if
- A small dog that fits the chart by chest girth
- You want the highest-rated listing of the 3
Don't buy it if
- Your dog sits between sizes on the chart
Storm and fireworks reports are the strongest, and the most divided
Owners of the large ThunderShirt, 12,962 ratings in all, write about storms more than any other trigger, describing dogs that stop hiding and shaking. The same listing collects the clearest reports of the wrap failing, and of owners unable to fasten it on a panicking dog.
Both points lead to the same practice: fit the wrap on calm days first, so it is familiar and quick to fasten before a storm arrives. The wider plan for fireworks nights matters more than the wrap alone: a quiet room, masking sound and a long-lasting chew.
ThunderShirt for Dogs Calming Anxiety Vest, Large
4.2 across 12,962 ratings, where the storm reports are strongest and the difficulty of fastening it comes up most.
Current price shown on Amazon. We may earn a commission.
| Size | Large |
|---|---|
| Evidence | 12,962 ratings |
| Watch | Fastening difficulty reported |
4.2 across 12,962 ratings, where storm-specific praise is most common. It is also where owners most often say the wrap did not work, or was close to impossible to put on.
For a large dog, practise the fastening on a calm afternoon. A fit that is easy on a relaxed dog becomes a struggle once the dog is frightened.
Buy it if
- Storms rather than separation are the trigger
- A large dog that tolerates a coat
Don't buy it if
- A dog that resists being handled around the chest
Cheaper wraps rate lower on thinner evidence
The nearest well-reviewed alternative, the Mellow Shirt calming wrap, rates 3.9 across 10,528 ratings, with owners reporting that sizes run large. Unbranded anxiety vests appear in the same search results with far fewer ratings, and none has an evidence base close to the ThunderShirt’s.
What this page cannot tell you is whether a ThunderShirt will calm a particular dog. Owner reports show a product that splits dogs into responders and non-responders, and nothing in them predicts which group a dog is in. A dog whose fear causes injury or escape attempts needs a vet, and a wrap is not a substitute.