One tape measure, two numbers, and the reason most harnesses are bought one size too big.
A harness fits by the chest, not the weight. Two dogs of 20 kg can be a size apart.
Measure the widest part of the chest
Run the tape round the ribcage just behind the front legs. Keep two fingers under it. That number picks the size.
Check the neck
The front strap should sit on the breastbone, not the throat. If the size that fits the chest is loose at the neck, go with the chest and tighten the neck strap.
Between sizes
Choose the smaller one if your dog is still growing out of puppy fat, the larger one for thick winter coats. Either way, returns are free for 60 days.
More from the shop.
How long a bag of kibble really lasts
The maths on the back of the bag, done properly for a 9 kg beagle, and why we pack the next bag before you run out.
The cat cave, week by week
Most cats sit on top of a felt cave for a week before they go in. A diary of one cat who took eleven days.
Bath day, with fewer towels
Brush first, rinse twice, and keep one towel for the shake. What the shop learned from washing a cockapoo every month.