How to use the collar and harness size calculator
- Measure your dog’s neck where the collar sits, with a soft tape.
- Measure the chest girth, the widest part of the ribcage just behind the front legs.
- Tick the box for toy and small dogs under 10 lb (4.5 kg).
- Read the collar size to buy, the range an adjustable collar should cover, and the harness size.
No soft tape? Use a piece of string, mark it, and measure the string with a ruler.
The formula
Collar size = neck + 2 in (or + 1 in for toy dogs). This leaves room for the two-finger check: you should fit two fingers between the collar and the neck. Brand guides commonly add 1–2 inches.
Adjustable collars should cover from the neck size up to a little more than the collar size, so you have room to adjust as your dog grows or its coat changes. The calculator shows neck to neck + 4 in.
Harness size uses Ruffwear’s published Front Range chart, by chest girth:
| Chest girth | Size |
|---|---|
| 13–17 in (33–43 cm) | XXS |
| 17–22 in (43–56 cm) | XS |
| 22–27 in (56–69 cm) | S |
| 27–32 in (69–81 cm) | M |
| 32–42 in (81–107 cm) | L/XL |
It is one brand’s chart, used here because it is widely sold and clearly published. Use your own brand’s chart if it is different.
Tips
- Between sizes? For a growing puppy, choose the larger size and adjust it down. Ruffwear gives the same advice.
- Re-measure puppies every few weeks.
- Harness fit check: you should fit two fingers under every strap, and it should not rub behind the front legs.
- Shopping for a crate too? The dog crate size calculator works from two measurements.
Sources
- Ruffwear: Front Range harness size chart and “The Size Is Right” measuring guide (two-finger fit).
- Pet collar makers’ sizing guides (neck measurement plus 1–2 in).
Frequently asked questions
How do I measure my dog for a harness?
Wrap a soft tape measure around the widest part of the chest, just behind the front legs (the girth). It should be snug but not tight. Most harness brands size by this chest girth, so use it with the brand’s own chart.
What size harness for my dog?
Measure the chest girth and match it to the maker’s chart. Ruffwear’s Front Range chart, one widely sold brand, lists 13–17 in is XXS, 17–22 in XS, 22–27 in S, 27–32 in M and 32–42 in L/XL. Other brands differ, so always check theirs.
How do I measure my dog's collar size?
Measure around the neck where the collar sits, usually just below the head. Then add about 2 inches (5 cm), or about 1 inch for very small dogs, so you can fit two fingers under the collar.
What size harness for a 20 lb dog?
Weight is only a rough guide because body shapes differ, so measure the chest girth around the widest part of the ribcage and match it to the maker’s chart. A deep-chested dog may need a bigger size than its weight suggests.
How tight should a dog collar be?
Snug enough that it cannot slip over the head, loose enough that you can fit two fingers comfortably between the collar and the neck, as Ruffwear’s fitting guide puts it. Check puppies’ collars every week because they grow fast.