Take two measurements: the chest, around the deepest part just behind the front legs, and the length, from the crook of the neck to the start of the tail. The chest is the one that decides the size.
Measure the chest snugly, because our garments are fitted and stretch to sit neatly on your hound. For the length, have your hound's head raised and measure along the back to an imaginary line at their backside, where the tail starts.
Measure the dog, not an old tee. A tee that has relaxed with wear isn't a reliable guide.
Then pop both numbers into the size finder on our size chart page. If the chest and length point to different sizes, go with the chest, and if the chest sits right between two sizes, go up.