Most harness sizing mistakes start with weight. Weight helps, but the number that really matters is how far around your dog's chest is. This guide shows you how to measure it, how to read a size chart, how to use weight to choose between two sizes and how to check the fit once the harness is on.
What you need
- A soft tape measure, like the kind used for sewing. No tape? Use a piece of string and a ruler.
- A few treats, and a helper if your dog wiggles.
- A pen and paper to write the number down in inches.
How to measure your dog's chest
- Have your dog stand on all four legs on level ground, head up in a relaxed way.
- Find the widest part of the chest. It is the ribcage just behind the front legs, about an inch or two back from where the legs meet the body.
- Wrap the tape around the chest and back at that spot. It should be snug against the coat, but not squeezing.
- Check that the tape is level and not twisted, then read the number where the end meets the tape.
- Using string? Pinch or mark the spot where it meets, then lay the string flat against a ruler.
- Measure two or three times. Dogs move, and the numbers can drift a little.
With a thick or fluffy coat, press gently so the tape sits against the body without crushing the fur.
Chest vs. weight: which one to trust
Chest girth is what the harness has to fit around, so start there. Weight is a rough check. Two dogs can weigh the same and be built very differently, one deep-chested and one barrel-chested. That is why the weight ranges on a size chart overlap.
Here is the supplier's size chart for our Reflective Dog Harness with Handle:
| Size | Chest | Dog weight |
|---|---|---|
| S | 13–24.8 in | 13–29 lb |
| M | 15.7–28.3 in | 26–53 lb |
| L | 18.5–33.9 in | 40–75 lb |
| XL | 21.7–39.4 in | 73–104 lb |
Look at the chest column first. If your dog's chest falls in one size only, that is your size. If it falls in two, use weight to narrow it down. Pick the size where your dog's chest sits closest to the middle of the range. That leaves the straps room to adjust both ways, tighter or looser. A chest measurement near the very top of a range leaves you no room to let the straps out. One near the very bottom leaves you no room to take them in.
A worked example
Say your dog measures 23.5 inches around the chest and weighs 38 pounds.
- Chest: 23.5 in fits both Small (13–24.8) and Medium (15.7–28.3).
- Weight: 38 lb is inside Medium (26–53 lb) but above Small (13–29 lb).
- Middle of the range: Small's middle is about 18.9 in, so 23.5 is near the top of its range. Medium's middle is about 22 in, so 23.5 sits close to the center.
Both checks point to Medium. If chest and weight ever disagree, go with the tape measure.
The two-finger fit check
Put the harness on, buckle it and adjust the straps. Then slide two flat fingers between each strap and your dog's body.
- Two fingers fit with a little wiggle room: good.
- Three or more fit: too loose. Tighten the straps.
- Two fingers will not fit: too tight. Loosen the straps, or try the next size up.
Check again after a few steps of walking, since straps can shift. The Reflective Dog Harness with Handle has adjustable straps and quick-release buckles, so you can fine-tune the fit on your dog.
Signs a harness is too tight or too loose
Too tight
- You cannot slide two fingers under the straps.
- The straps ride up into your dog's armpits.
- Your dog's front legs look held back, or the steps look shorter than usual.
- You see flattened fur or marks where the straps sat after you take it off.
Too loose
- You can fit three or more fingers under a strap.
- The harness slides to one side, twists or shifts back toward the hips.
- The chest strap gaps or sags.
- Your dog can back out of it.
If the harness is loose on its tightest setting, move down a size. If it is tight on its loosest setting, move up one.
Check the fit as puppies grow
Measure your puppy's chest as it is now, not as you guess it will be. A harness bought with lots of room to grow is easy to slip out of. Re-measure every few weeks, and any time the harness starts to look snug. You may need to move up a size more than once in the first year. Adult dogs need a recheck too, after a big change in weight or a thick winter coat.
A safety note
A harness is for walks and supervised time. Watch your dog while it is wearing one, and take it off when you are not there to supervise, such as when your dog is alone at home or in a crate.
The harness in our shop
- Reflective Dog Harness with Handle: padded mesh lining, adjustable straps, a back grab handle, reflective stitching and quick-release buckles. The supplier lists polyester as the material. It comes in black, red and orange, in sizes S to XL.
- A soft tape measure, or string and a ruler.
The supplier sells this harness as a no-pull design. This guide is about fit only, and we cannot promise how any harness will change the way your dog walks.