A harness that fits well keeps your dog comfortable and safe on walks; one that is too loose can slip off, and one that is too tight can rub or restrict movement. Harnesses are sized by chest girth, the distance around the widest part of the ribcage, not by breed or by weight. Enter your dog’s girth and pick a brand, and this calculator returns the size from that brand’s published chart.
How to use the dog harness size calculator
- Measure the girth. Wrap a soft tape around your standing dog’s chest, just behind the front legs, at the widest point. Keep it snug but not tight, with two fingers able to slide underneath.
- Choose the unit (inches or centimetres) and enter the number.
- Pick the chart that matches the harness you plan to buy.
- Read the size. The result shows the girth range for that size, and any neighbouring size that also covers your dog’s girth.
The sizing formula: how the size is chosen
match = every size with lower limit ≤ girth ≤ upper limit
if two or more match → choose the larger (second) one
Both brands advise a size up for a dog that is between sizes. Ruffwear’s sizes end exactly where the next begins, so a girth on the boundary matches two sizes and the larger is chosen. PetSafe’s sizes overlap in several places, so more than one can match; when there are three the middle one is picked. The tables below are the published charts (retrieved 2026-10-15), with the centimetre columns calculated by multiplying inches by 2.54.
Ruffwear harness, apparel and pack sizes
| Size | Girth (in) | Girth (cm) |
|---|---|---|
| XXXS | 9 – 13 | 23 – 33 |
| XXS | 13 – 17 | 33 – 43 |
| XS | 17 – 22 | 43 – 56 |
| S | 22 – 27 | 56 – 69 |
| M | 27 – 32 | 69 – 81 |
| L | 32 – 36 | 81 – 91 |
| XL | 36 – 42 | 91 – 107 |
PetSafe Easy Walk harness sizes
| Size | Girth (in) | Girth (cm) | Approx. weight |
|---|---|---|---|
| Petite | 12 – 17 | 30 – 43 | under 10 lb |
| Petite / Small | 13 – 18 | 33 – 46 | 10–15 lb |
| Small | 15 – 21 | 38 – 53 | 15–25 lb |
| Small / Medium | 19 – 26 | 48 – 66 | 20–30 lb |
| Medium | 22 – 32 | 56 – 81 | 25–50 lb |
| Medium / Large | 24 – 34 | 61 – 86 | 40–65 lb |
| Large | 27 – 40 | 69 – 102 | 65–95 lb |
| Extra Large | 32 – 49 | 81 – 124 | 90+ lb |
Worked example
A dog has a chest girth of 25 inches, shopping for the PetSafe Easy Walk.
- 25 in lies in Small / Medium (19–26), Medium (22–32) and Medium / Large (24–34).
- With three matches the middle one is taken: Medium, which covers 22–32 in and is meant for dogs of roughly 25–50 lb.
- The neighbouring sizes that also cover 25 in are Small / Medium, Medium / Large.
Fitting a harness after you choose a size
- Two-finger rule: you should be able to slide two fingers between the straps and your dog’s body.
- Check movement: the shoulders must move freely and the straps should not rub behind the front legs.
- Coat thickness: a thick coat can make a tape reading read larger than the body; press the fur flat while measuring.
- Re-measure puppies often, as growth is fast in the first year.
Harness charts in this guide cover Ruffwear and PetSafe only. Other makers, such as those making lightweight or step-in styles, publish their own tables, and ranges differ. This page is general guidance and does not replace the fitting instructions that come with the product.
Sources
Every figure above comes from these pages, read directly on the dates shown.
- Ruffwear — sizing guide for harnesses, apparel and packs — checked 2026-10-15
- PetSafe — Easy Walk harness fitting guide and sizing chart — checked 2026-10-15
Frequently asked questions
How do I measure my dog for a harness?
Measure the girth, the widest part of the chest just behind the front legs, with a soft tape that is snug but lets you slide two fingers underneath. Both brands on this page size by girth.
What if my dog is between two sizes?
Ruffwear and PetSafe both say to choose the larger size when a dog is truly between two. Where the chart ranges overlap the calculator picks the larger of the two lowest overlapping sizes and lists the others as neighbouring sizes.
Is weight a reliable way to choose a harness?
No. Weight is only approximate. PetSafe states this on its chart, and breeds with deep chests or thick coats can be much larger in girth than their weight suggests. Use girth first.
Do puppies need a bigger harness to grow into?
Ruffwear advises sizing to the current measurements and replacing the harness as the puppy grows, because gear that is too big can chafe or slip. Re-measure every few weeks.
Can I use one brand’s size on another brand’s harness?
No. Chart ranges differ, as the two tables here show. Use the matching chart for the brand you buy. Related: Baby Clothes Size Calculator shows the same approach for children.