Short answer
A harness is too small if it only does up on its loosest setting, presses into the skin or the armpits, sits across the throat, or leaves marks or rubbed fur. It is too big if it twists or slides round, has gaps a leg could slip through, or your dog can back out of it even with every strap at its tightest.
Small, big, or just badly adjusted?
This article answers one question from our complete guide to how a dog harness should fit.
Ruffwear notes that if gear is too large or too small, "you might see some chafing or slipping"1. Before deciding a harness is the wrong size, check the adjusters. If there's still room to loosen or tighten, the harness may just need adjusting. If every adjuster is already at its limit and the fit is still wrong, it's the wrong size.
Signs a harness is too small
- You can only just do the buckles up, or only on the loosest setting.
- The straps press grooves into the coat or leave dents after you take it off.
- The girth strap sits up in the armpits because there isn't enough strap to sit further back.
- The front strap sits high on the throat instead of on the breastbone. A good harness avoids pressure on the neck2.
- Red marks, rubbed fur or bald patches behind the front legs, under the chest or around the neck. Julius-K9 warns that a belly strap that is too tight can be uncomfortable and the buckle may rub the skin3.
- Your dog's stride looks shorter than without the harness, or it walks stiffly.
- Your dog scratches or bites at the straps, or seems keen to get it off.
Sore skin?
If the skin is sore, broken or bald under a strap, stop using the harness and see your vet.
Signs a harness is too big
- It twists or slides round so the lead clip ends up on one side.
- There are gaps between strap and body that a leg could slip through.
- In the escape test (a gentle pull backwards and up on the lead) it slides over the shoulders or ribs, or an over-head loop comes up over the ears. Julius-K9 warns that with straps too loose a dog "might be able to back out of it"3.
- The front panel droops between the front legs or flaps when your dog trots.
- Every adjuster is pulled to its tightest and there's still slack.
- Excess strap hangs down and flaps, or the buckles sit in odd places, such as on the spine or under the chest.
Right size, wrong shape
Sometimes a harness is the right size for your dog's chest but the wrong shape for its body. The signs look like a sizing problem, but changing size won't fix them.
- Deep chest, narrow waist (Whippet): a harness that fits the ribs can still slide backwards off the waist. We suggest a design with a second strap further back.
- Long back, short legs (Dachshund): the girth strap may end up in the armpits whatever size you buy. A different style may sit better.
- Broad chest, short neck (Bulldog): a straight-across front may press on the shoulders or ride up to the throat. Battersea recommends a Y-shaped front2. For flat-faced breeds like the Bulldog, the Royal Kennel Club advises a harness instead of a collar "to avoid putting pressure on their airway"4, so a front that rides up is a real problem.
What to do next
- Take the harness off and re-measure your dog's chest round the widest part of the ribcage. Our measuring guide shows how.
- Compare the number with the brand's size chart, or put it into our size finder, which checks it against every brand we cover.
- If your dog is between two sizes, read the "between sizes" section of your breed's harness guide, such as the Border Collie harness guide.
- If the size is right but the fit is still wrong, the style may not suit your dog's shape. Try a different design.
- Once you have the right harness, fit it using the brand's instructions and our five-minute fit check.
Between two sizes
Size charts often overlap, so a chest measurement can fall in two sizes. In that case, the deciding question is what the adjusters can do. We suggest choosing the size where your dog's measurement sits nearer the middle of the range, so you can loosen or tighten it as the coat changes.
For a growing puppy that is truly between two sizes, Ruffwear says to choose the larger size1. Only do that if the larger size can be tightened to a safe, snug fit now: a loose harness is the easiest kind to escape from.
Breed harness guides
Every breed fits a harness a little differently. These guides cover the sizes in each brand, how to measure that breed, and the styles that suit it.
- Whippet harness sizeSizes by brand, measuring and fit
- Standard Dachshund harness sizeSizes by brand, measuring and fit
- Bulldog harness sizeSizes by brand, measuring and fit
- Border Collie harness sizeSizes by brand, measuring and fit
Find your dog's harness size All breeds
Questions
How do I know if my dog's harness is too small?
It only fastens on its loosest setting, presses into the skin, sits in the armpits or on the throat, or leaves marks or rubbed fur. If the skin is sore, stop using it and see your vet.
How do I know if my dog's harness is too big?
It twists or slides round, has gaps a leg could get through, or slides over the shoulders when you pull gently backwards on the lead, even with every strap at its tightest.
My dog backed out of its harness. Is it too big?
Possibly, or it may just be too loose. Tighten the straps and repeat the escape test. If it still slides off at the tightest setting, it's too big or the wrong shape for your dog.
Should I size up or down if I'm not sure?
Re-measure first. Then choose the size where the measurement sits nearer the middle of the range, and check your brand's own advice for dogs between sizes.
The harness leaves marks in my dog's fur. Is that normal?
Dents that stay after you take the harness off usually mean it's too tight. Loosen it and check again. If the skin underneath is red or sore, see your vet.