How to measure your dog to buy clothes online: step-by-step guide

Buying clothes for your dog online has one single trap: sizing. It's not quality, it's not price, it's not the pattern — it's the size. Every week in the shop we see returns that could have been avoided with two minutes of a measuring tape before buying. And it's not because customers are careless: it's because nobody has properly explained what to measure, how to measure and what to do if the dog falls between two numbers.

This article is the practical guide that saves you the return. I'll tell you the three measurements you need to take before buying any clothing item for your dog, how to take them properly, the specific sizing of the clothing brands we stock at Mascoboutique (Milk & Pepper, Fashion Dog and Alqo Wasi), what to do if your dog is right between two sizes, and the most common mistakes I see when someone returns a garment. Do this once and you'll get it right every time.

The three measurements you need before buying any garment

Before adding any garment to the basket, three numbers on a piece of paper. But before I get into each one, a key nuance: the measurement that matters most is NOT the same on a harness as on a jumper or a coat. On a harness, the fastening goes around the chest, so chest girth is queen. On a coat, a jumper, a raincoat or a t-shirt, what the garment has to cover is the back — and there the main reference is back length. Chest girth also matters in clothing, but since most garments are stretchy or have an adjustable closure, it usually fits fine except in dogs with a particularly wide chest (French bulldog, pug, Boston terrier). We treat those breeds separately below.

With that nuance clear, these are the three measurements — always write down all three and you'll know which one to look at depending on what you're buying:

Back or spine length (the reference in clothing)

Back length —also called spine length— goes from the base of the neck (where a collar would sit) to the base of the tail. Do NOT include the tail. It's the main measurement for choosing size in t-shirts, jumpers, coats, raincoats and any garment that covers the dog's body. It determines whether the garment covers what it needs to cover without covering the tail or the rump.

The correct way to measure it: dog standing firmly and relaxed, with all four paws on the ground (no sitting, no lying down, no being held in your arms — the back must be in its natural position). The tape goes from the point where the neck ends —not from the nape, not taking part of the neck— to the point where the tail begins. In other words, the measurement runs along the spine only. The tail doesn't count, not one centimetre.

The most common mistake I see: people measure from the nape to the tip of the tail. That measurement is useless — it's something else and always gives a bigger number than what you need. In brands like Milk & Pepper, the size number equals the back length in centimetres directly, so this figure when taken properly is the most practical one.

A shop trick to check if you've measured correctly: look at the number you got and compare it with your dog's weight. If your dog weighs 2.5 kg and you're getting a back length of 38 cm, something doesn't add up — a toy dog of 2.5 kg is usually around 26-28 cm. If the two figures don't match, you've almost certainly taken part of the neck, or the dog was hunched, or you've gone too far back. Repeat the measurement.

And now a real shortcut we give in the shop to clients who can't measure their dog. In dogs with normal proportions —that is, without extreme proportions like brachycephalics— there's a fairly reliable correlation between weight and back length. The correlation stays fairly linear in the medium range; at the extremes (very tiny dogs of 2-2.5 kg or medium breeds of 8-13 kg) the pattern varies more and you should really measure. That's why our size guides always show both references —measurement in centimetres AND approximate weight—, so the customer can use whichever is more convenient. But if you can measure your dog well, do it — the real measurement always helps fine-tune. (Further down I'll give you the specific weight-size scale we use with Fashion Dog.)

Chest girth (the reference in harnesses)

Chest girth is taken at the widest part of the dog's rib cage, just behind the front legs — where the ribcage reaches its maximum width. It's the key measurement for choosing a harness (because the harness fastening goes precisely around the chest) and an important check measurement in clothing: if your dog has a wider chest than normal, you need to verify it before buying any closed garment.

In stretchy clothing, most dogs pass without problems because the fabric gives. The exception is breeds with special proportions: French bulldog, pug, Boston terrier, pug — the brachycephalics with a very wide torso relative to a short back. In those breeds, checking chest girth is as important as back length, because a garment that fits well on the back may not close underneath.

Neck girth

Neck girth is taken around the dog's neck right where a collar would sit. It's the least critical of the three for clothing —in sleeveless stretchy t-shirts it hardly matters—, but it becomes decisive on collars (where it IS the measurement) and in garments with high collars: turtleneck jumpers, hoodies, some coats with lapels. There, measure it without fail.

How to take the measurements: step by step

You need a flexible measuring tape (sewing type) or, failing that, a piece of string and a ruler. No rigid carpenter's tape measures — they don't wrap around the dog's body properly.

A shop trick before you start: the dog has to be standing, relaxed and with all four paws on the floor in a normal position. No lying down, no sitting, no picking them up. If your dog moves around a lot, ask someone to entertain them with a treat so they don't wriggle.

The concrete steps:

• Chest girth — run the measuring tape just behind the front legs, wrap it around the torso and check that the tape passes under the chest without slipping under the armpit. The tape sits flush with the fur but without tightening. Note down in centimetres.
• Back or spine length — with the dog standing firmly (not sitting, not lying down), place the end of the tape EXACTLY where the neck ends, don't take part of the neck. Run it along the spine to the exact point where the tail begins. Do NOT count the tail. Note down in centimetres. Check that the resulting number matches the dog's weight; if it doesn't add up, measure again.
• Neck girth — wrap the tape around the dog's neck where the collar would sit, neither too high nor too low. The tape sits comfortably, not tight. Note down in centimetres.
• Dog's weight — put them on the scale. If they're small, weigh them in your arms and subtract your weight. This figure is always requested by the size guide along with the measurements.

With those four figures (chest girth, back length, neck girth and weight), you open any size guide and compare. That's all you need.

Sizes are not universal: what you need to know about each brand

Here's the mistake I see most: comparing the size that worked in one brand with another. It does NOT work. Each brand has its own sizing and, although the result may be similar, the numbers don't match. Here's a summary of the three premium brands we sell most at Mascoboutique so you know how they work.

Milk & Pepper

The Parisian firm Milk & Pepper works with NUMERIC sizing. Sizes go from 26 to 45, and the number roughly indicates the BACK LENGTH in centimetres. It's the easiest system to understand: if your dog measures 30 cm along the back, size 30 is your starting point. And from there, check the chest girth to make sure it also fits (the size guide of each specific garment shows the equivalence).

For a mini chihuahua or very small dachshund: between 26 and 28. Standard chihuahua, yorkie, toy bichon: 28-30. French bulldog puppy or adult dachshund: 32-36. Adult French bulldog, young cocker, small poodle: 38-42. 45 is the maximum. Milk & Pepper does NOT fit medium-large dogs.

Fashion Dog

The Italian brand Fashion Dog is another of the jumper and coat brands we stock. Its sizing is also NUMERIC, with a very similar logic to Milk & Pepper: the number correlates with the dog's back length. And because the pattern is very well cut, the weight-size scale we use in the shop is especially reliable with them.

The weight→size equivalence we use with normal-pattern dogs is this: 3 kg goes in size 30, 4 kg in 33, 5 kg in 36, 6 kg in 39. At the extremes it stops being a linear rule and we have specific sizes: 2 kg in size 24, 2.5 kg in size 27, 7 kg in size 43, 8 kg in size 47, and up to size 51 for dogs of 9-13 kg. If your dog fits any of those weights and has a normal pattern, that size will work. If it doesn't add up (e.g. a 6-kg dachshund with a very long back), measure.

An internal note: we're preparing an own Mascoboutique line that will use this same pattern, precisely because it's the one that fits our repeat customers best.

Alqo Wasi

The Peruvian brand Alqo Wasi —jumpers and ponchos in alpaca wool handmade in Peru— works with LETTER sizing: XXS, XS, S, M, L and XL. It covers from the tiniest toy to medium-large dogs, and it's a useful scale because it doesn't fall short at the top, something that does happen with brands designed only for toy breeds.

The approximate equivalence, in back length, is: XXS ≈ 26 cm, XS ≈ 31 cm, S ≈ 37 cm, M ≈ 43 cm, L ≈ 50 cm and XL ≈ 57 cm. Translated to specific breeds: a standard chihuahua or a mini yorkie usually goes in XXS or XS; an adult French bulldog fits S or M depending on the individual; a cocker or a medium poodle needs the L; and XL covers medium-large breeds such as miniature bull terrier or similar. As always, verify on the specific product page because each model has its own table.

What to do if your dog is between two sizes

It's a classic situation: you measure the dog, open the guide and see that they fall right between S and M, or between 30 and 32. The short answer, the one I always give in the shop, is: the smaller size.

Why? Because in dog clothing the exact fit always looks better than the loose one. A garment that's too big dances around, twists, gets caught by the paws and can ride up at the back, leaving the belly exposed. A garment with two cm of ease over the chest still fits comfortably. One with two cm too much doesn't.

The only exceptions to this rule are:

• If your dog is in a weight-change phase (a puppy that's still growing or an adult dog that has slimmed down): go with the larger one, so it lasts longer.
• In winter garments with padding (thick puffers): the larger one, because the volume of the filling reduces the interior.
• If you're buying something with a closed sleeve and the dog has a VERY wide chest relative to neck and back (typical French bulldog, pug, Boston terrier): consult the shop because you may need the larger size.

For everything else, and especially in t-shirts, jumpers and harnesses: the smaller one. And if you're unsure, WhatsApp us with chest girth, back length, neck girth and the dog's weight. In two minutes we'll tell you which size is the right one.

The most common mistakes when buying dog clothes online

The mistakes I see every week when a return comes in:

• Trusting weight alone in breeds with special patterns. In normal-pattern dogs weight is a good shortcut (our guides include it precisely for that reason). But when the breed has peculiar proportions —dachshund with very long back, French bulldog with wide torso, greyhound with deep chest—, two dogs of the same weight need different sizes. In those cases always measure.
• Measuring with the tape tight. The tape sits flush with the fur but WITHOUT tightening. If you measure by pulling tight, the size that comes out is smaller than the real one and you get a tiny garment.
• Counting the tail in the back length. It's the most common mistake. The tail never counts — the length is measured from the neck to the base of the tail exclusively.
• Extrapolating sizes between brands. The S in Alqo Wasi doesn't equal any specific Milk & Pepper size nor any Fashion Dog size — each brand has its pattern and its table. Always check the specific product page.
• Buying the larger one "in case they grow". Dogs are adults by 8-12 months. Except for puppies that are known to grow a lot, buying the larger one is wasting money.
• Not measuring an adult dog again. Older dogs lose muscle and slim down. A dog's size at three years old may not be the same at ten. If it's been a while since you bought clothes, measure again before.

In summary: measure once, buy well

If you've made it this far with the doubt of how to measure your dog properly to buy clothes online, this is the summary:

• Three measurements: back length (the reference in clothing), chest girth (the reference in harnesses) and neck girth. Plus weight.
• Clothing (t-shirts, jumpers, coats, raincoats): look mainly at back length. Chest usually fits due to fabric elasticity — only verify if your dog has a special pattern (French bulldog, pug, Boston, pug).
• Real shortcut in normal-pattern dogs: weight correlates well with back length (3 kg ≈ 30, 4 kg ≈ 33, 5 kg ≈ 36, 6 kg ≈ 39). That's why our size guides always include approximate weight in addition to measurements — so you can use the reference that's more convenient for you.
• Harness: look mainly at chest girth. That's where the fastening goes.
• Collar: look mainly at neck girth.
• Flexible measuring tape, dog standing relaxed, tape flush with fur without tightening.
• Brand-specific size guide — don't extrapolate.
• Milk & Pepper: numeric, from 26 to 45, the number equals back length in cm.
• Fashion Dog: numeric too, with a very reliable weight-size scale in normal patterns (3 kg → 30, 4 kg → 33, 5 kg → 36, 6 kg → 39, and extremes 2 kg → 24, 2.5 kg → 27, 7 kg → 43, 8 kg → 47, 9-13 kg → 51) less linear.
• Alqo Wasi: letter sizing, from XXS to XL — covers from toy (≈26 cm back length) to medium-large (≈57 cm).
• If your dog falls between two sizes, go with the smaller one (except for growing puppies or thick winter garments).
• If in doubt, WhatsApp the shop with the three measurements + weight. In two minutes we get it right.

And to see the clothing catalogue on sale, take a look at our full dog clothing section. All garments have their specific size guide on the product page.

About the author

Mar is the founder of Mascoboutique. What started as an idea to dress and equip her own dog became, over the years, a reference boutique in Madrid for families with dogs. Every t-shirt, harness or accessory that comes into the shop passes through her hands first: she tests materials, checks stitching and pictures the dog that's going to wear it. That same demanding standard applies to the blog: here we don't recommend what sells best, but what she herself would put on her own dog.