What size collar for a Jack Russell?
Most adult Jack Russells need a collar in the region of 30 to 40cm around the neck, though the breed's size varies enough that measuring your own dog is far more reliable than going by breed alone. Measure snugly around the neck where a collar would sit, then check that against the size range on the collar itself.
How to measure your Jack Russell
Wrap a soft tape measure around the middle of your dog's neck, where a collar naturally sits rather than right up near the ears or down near the shoulders, and pull it snug without tightening it. Add roughly two centimetres to that measurement to allow room for two fingers to fit comfortably underneath the fastened collar.
If you do not have a soft tape measure, a length of string works just as well — wrap it the same way, mark where it meets, then measure the string flat against a ruler.
Why breed size alone is not enough
Jack Russells vary more in size than their compact reputation suggests, with adult neck sizes commonly falling somewhere between about 28 and 42cm depending on the individual dog's build. A wiry-coated, leggier Jack Russell and a stockier one can differ enough that a single "Jack Russell size" recommendation is not reliable on its own.
Coat thickness matters too — a collar that fits well on bare skin can sit differently once a thicker coat is accounted for, so measure with your dog's coat in its usual condition rather than freshly clipped or unusually fluffy.
Checking the fit once it's on
A well-fitted collar allows two fingers to slide flat underneath comfortably, without being loose enough to slip over the head or so tight that it presses on the throat. Check the fit again after a few weeks, particularly on a younger dog who may still be growing.
If your Jack Russell is a determined escape artist, a snugger fit paired with a well-fitted harness for walks gives extra security, since a collar alone relies on the neck measurement staying accurate day to day.
The sizes we stock
Everything below is in stock with us, priced with delivery worked out, and packed and posted by hand in the UK.
Real-Time GPS Pet Tracker
A compact GPS tracker that clips to most collars for real-time location, geofence alerts and find-me sound.
£29.99
Waterproof Dog Harness, Collar & Lead Set
A sturdy waterproof harness, collar and lead set that keeps walks tidy and your dog under control.
From£7.99
Smart Bluetooth Tracker Tag (Works with Find My)
A compact Bluetooth tracker that pairs with Apple Find My for global positioning, with left-behind alerts and the option to share tracking with up to six people. Clip it to a pet collar, keys or bag so nothing goes missing.
From£7.99
Flea & Tick Repellent Collar for Dogs & Cats
An adjustable 70cm repellent collar, water-resistant and trimmed to fit either a cat or a dog, giving day-to-day deterrence against fleas and ticks with no drops to apply.
£7.99
Common questions
- What size collar does a Jack Russell puppy need?
- A growing puppy needs checking and re-measuring every few weeks rather than one fixed size, since neck measurements can change quickly. Start with an adjustable collar with plenty of room to size down, and check the fit regularly as your puppy grows.
- How do I know if my Jack Russell's collar is too tight?
- If you cannot comfortably fit two flat fingers underneath the fastened collar, it is too tight. Signs of a too-tight collar can include rubbing, hair loss around the neck, or your dog scratching at it more than usual.
- Is a wide or narrow collar better for a Jack Russell?
- A moderate width usually suits the breed's compact size well — wide enough to sit comfortably without being so wide it feels heavy or restrictive on a smaller dog. Very narrow collars can dig in more if your dog pulls.
Sources
Written against guidance published by UK veterinary and welfare organisations. Always confirm specifics with your own vet.
Written by Matt Garnett, who runs Giddy Pets and is a lifelong pet owner — not a vet. This is general information, not veterinary advice, and it cannot replace an examination by the vet who knows your animal. How we write these guides.