Coat makers genuinely disagree on which measurement matters, and it tracks the closure, not carelessness. A blanket-style coat with strap closures sizes on back length. A fitted coat with a zip or sleeves sizes on chest girth. Tell us which one this is, plus both measurements, and we size it the way that closure actually needs.
How dog coat sizing works
Search "dog coat size chart" against three different makers and you can get three different opinions on whether length or girth matters more, and it looks like nobody agrees. What is actually happening is that they are frequently describing different coats. A coat that wraps over the back and closes with adjustable straps can absorb a few inches of chest girth in those straps, so it is sized on back length. A coat with a zip, sleeves or leg holes is cut from woven fabric that does not stretch, and a zip that will not close is a coat you cannot use at all, so it is sized on chest girth instead.
Neither maker is wrong. They are answering the sizing question for a different closure, and a chart that does not ask which one you have is skipping the step that actually matters.
The formula
Blanket coat (strap closure) → size from the BACK LENGTH chart, chest checked against the straps
Fitted coat (zip, sleeves or leg holes) → size from the CHEST GIRTH chart, length reported as a consequence
Worn over a harness → add 1 in to the chest before either lookup
Both charts run XS through XL and are shared with our dog sweater size chart: back length bands are 8 to 10 in (XS), 10 to 14 in (S), 14 to 18 in (M), 18 to 22 in (L), and 22 to 28 in (XL). Chest girth bands are 12 to 16 in (XS), 16 to 22 in (S), 22 to 28 in (M), 28 to 34 in (L), and 34 to 42 in (XL), the same chest bands our dog harness size chart uses.
Worked example
Blanket coat, no harness: a 20 in back lands in the L band (18 to 22 in), so the coat is an L. A 24 in chest lands in the M band, one size smaller than the back length, so the straps will be set toward their tightest to close around it, which is exactly what a strap closure is for.
Fitted coat, worn over a harness: a 28 in chest becomes 29 in once the harness's 1 in is added, which lands in the L band (28 to 34 in). A 26 in back lands in the XL band on its own, one size larger than the chest, so the L coat will run a little short and leave the hips less covered than the chest measurement alone suggests.
How to measure
Back length runs from the base of the neck, roughly where a collar sits, to the base of the tail, not the tip. Keep the dog standing square. Measuring from the skull instead of the neck is the most common error and adds a few inches that sends you up a size for no reason.
Chest girth is the widest part of the ribcage, just behind the front legs, with the tape snug against the fur but not compressing it. Our dog harness size chart covers the same measurement in more detail. No tape measure handy: run a piece of string around the dog and measure the string against a ruler.
Why coat charts disagree, and what actually changes
The closure decides the primary measurement, and the coat's build changes what the sizing risk looks like. A blanket coat's failure mode is length: too long and it reaches past the base of the tail, drags, gets soiled, and the dog ends up sitting on it; too short and it leaves the hips out in bad weather. A fitted coat's failure mode is width: a snug chest on a woven, non-stretch coat only ever gets tighter, never more comfortable, which is why the advice at the top of a fitted coat's chest band is to size up rather than stay, the opposite of what a knit sweater tells you at the same spot.
Insulation changes the numbers a little too, though not the logic. An insulated coat is bulkier on the inside than a plain waterproof shell, so a chest measurement that reads snug on a shell can read genuinely tight once the lining is in the way. If you are choosing between the two for the same dog, favor the roomier read on a borderline chest measurement for the insulated version.
Coat versus sweater
They are not the same problem wearing two names. A knit sweater stretches and pulls on over the head, so it is sized on chest girth and a snug top-of-band fit is fine because the knit gives. A woven coat does not stretch and closes with hardware instead, so which measurement leads depends on that hardware: straps forgive a chest mismatch and let back length decide, while a zip or sleeves forgive nothing and put chest girth back in charge. The dangerous direction changes with the garment too: a sweater fails at the armholes and the belly, a coat fails at the shoulders (watch the dog walk: a tight coat there visibly shortens the stride) or at the length, never at the armhole the way a knit does.
Frequently asked questions
How do I measure my dog for a coat?
Back length runs from the base of the neck, where a collar sits, to the base of the tail, dog standing square. Chest girth is the widest part of the ribcage just behind the front legs, snug over the fur without compressing it. Which one decides the size depends on how the coat closes: back length for a blanket-style wrap, chest girth for a fitted coat with a zip or sleeves.
Why do dog coat charts give different sizing advice?
Because they are often sizing different kinds of coats, not disagreeing about the same one. A blanket coat's straps can absorb a few inches of chest, so the maker sizes it on back length. A fitted coat's zip or sleeves cannot absorb anything, so it has to be sized on the chest girth it actually has to close around.
What size coat for a dachshund or other long, low dog?
We will not invent a number for a specific breed, since published breed figures vary and were never independently checked. The build problem is a back length that reads well above the chest girth, so pick the coat style deliberately: a blanket coat sized on that long back may leave the straps loose around a narrow chest, while a fitted coat sized on the chest may come up short along the spine.
Are dog coat sizes the same between brands?
No. XS through XL are a typical ladder here, not a published standard, and each maker sets its own bands. The inches or centimeters on the listing are what travel between brands, not the letter.
My dog is between two coat sizes, which do I buy?
It depends on the closure. On a blanket coat, sizing is about back length: a coat that runs too long drags past the base of the tail and gets sat on, so only round up if the next size starts within about half an inch of your measurement. On a fitted coat, sizing is about chest girth, and because woven fabric does not stretch, near the top of a chest band you should round up rather than stay, the opposite of a knit sweater.
Should a dog coat cover the tail?
No. A coat that runs long enough to reach the base of the tail is already doing its job; going further just means excess fabric that drags, collects mud, and gets sat on. If a coat is riding well past the tail, that is a sign it runs long for this dog, not a feature to look for.
Do I need a bigger coat if my dog wears a harness underneath?
Usually about an inch more chest, since the coat has to close over both the dog and the harness strap across the chest. This page adds that inch automatically when you say the coat goes over a harness, and shows the arithmetic so you can check it.
What is the difference between this page and the dog sweater size chart?
Material and closure, the same pair of facts that split this page in two internally. This page covers woven coats and jackets, straps, zips, sleeves, no stretch. Knit clothes that pull on over the head, sweaters, hoodies, pajamas, tees, size differently because the fabric gives, and they get their own page: our dog sweater size chart.