Getting the right harness size is critical for your dog's safety, comfort, and your sanity. A poorly fitted harness can cause rubbing, allow escape, restrict breathing, or simply not work for training. Yet most people guess their dog's size or rely on weight alone—which is why returns are so common.
This guide will show you exactly how to measure your dog for a harness in three simple steps, what tools you need, common mistakes to avoid, and breed-specific tips that make all the difference. Whether you have a tiny Chihuahua or a large Labrador, you'll get the perfect fit first time.
Why Measuring Your Dog Properly Matters
Here's what happens when harness sizing goes wrong:
Too Small:
- Restricted breathing: Chest plate presses on airways (dangerous for flat-faced breeds)
- Rubbing and chafing: Creates sore spots, especially under arms
- Restricted movement: Limits shoulder mobility, causes discomfort
- Behavior changes: Dog refuses to walk or becomes reluctant
Too Large:
- Escape risk: Dog can back out or slip free
- Twisting and rotation: Harness shifts during walks
- Rubbing from movement: Loose straps cause friction
- Loss of control: Doesn't work for training or safety
The Cost of Getting It Wrong: UK harness returns cost you return postage (typically £3-£5), delay getting your dog into proper equipment, and waste time. More importantly, using an ill-fitting harness while waiting for the right size can cause injury or allow escape. Measure properly once, get it right first time.
Weight Alone Doesn't Work
Two dogs of the same breed and weight can have completely different builds:
- A lean, athletic Labrador vs a stocky, broad-chested Labrador
- A petite female Cocker Spaniel vs a large male
- An overweight Pug vs a fit Pug at the same weight
Weight is a rough guide. Measurements are what actually determine fit.
What You Need to Measure Your Dog
Before you start, gather these items:
Essential Tools:
- Soft fabric tape measure - The kind used for sewing. Available at any craft shop or online for £2-5. DO NOT use a metal tape measure (uncomfortable and inaccurate).
- Paper and pen - To record measurements immediately
- Treats - Keep your dog standing and cooperative
- Helper (optional but useful) - One person holds/treats, one measures
Don't have a fabric tape measure? You can use string or ribbon to measure around your dog, then measure the string with a ruler. Mark the string where it meets, then measure that length in centimeters. Not as easy, but it works in a pinch.
Best Time to Measure
- After exercise: Your dog is calmer and more cooperative
- Not after meals: Bloated stomach can affect chest measurement
- When relaxed: Not when excited or anxious
- Standing naturally: All four paws on the ground, normal posture
The 3 Key Measurements for Dog Harnesses
You need three measurements. Here's what they are and why they matter:
1. Chest Girth (Most Important)
What it is: The circumference around the widest part of your dog's ribcage
Where to measure: Just behind the front legs where the harness girth strap sits
Why it matters: This is THE critical measurement. Harness sizing is primarily based on chest girth. Get this wrong and nothing else matters.
2. Neck Circumference
What it is: The circumference around the base of the neck
Where to measure: Where a collar would normally sit
Why it matters: Ensures the neck strap isn't too tight (restricts breathing) or too loose (slips off)
3. Body Length (Sometimes Required)
What it is: The length from the base of the neck to the base of the tail
Where to measure: Along the spine from where neck meets shoulders to where tail starts
Why it matters: Some harnesses (especially for long-backed breeds like Dachshunds) require this to ensure proper coverage without riding up
Pro Tip: Always measure in centimeters for UK harness sizing. Most UK manufacturers use cm, and it's more precise than inches. If your tape measure shows both, use the cm side.
Step-by-Step: How to Measure Your Dog for a Harness
Step 1: Prepare Your Dog
- Have your dog stand naturally on all four legs
- Choose a flat, non-slip surface (not on a bed or sofa where they sink down)
- Keep them calm and still - use treats to encourage standing position
- If using a helper, have them hold your dog steady and give treats
Step 2: Measure Chest Girth
- Locate the widest part of the ribcage - this is typically 2-3 inches behind the front legs
- Wrap the tape measure around the ribcage at this point
- The tape should be snug but not tight - you should fit two fingers comfortably underneath
- Make sure the tape is level all the way around (not twisted, not angled)
- Record the measurement in centimeters
- Measure twice to confirm accuracy
Common Mistake: Measuring too close to the front legs (armpits) gives an inaccurate reading that's too small. The widest part of the chest is typically 5-8cm behind where the legs attach. If in doubt, measure slightly further back rather than too close to the legs.
Step 3: Measure Neck Circumference
- Find the base of the neck where it meets the shoulders (where a collar sits)
- Wrap the tape measure around the neck at this point
- Again, apply the two-finger rule - snug but not tight
- Ensure tape is level (not pulling up toward ears or down toward chest)
- Record measurement in centimeters
- Measure twice to confirm
Step 4: Measure Body Length (If Needed)
- Have your dog stand naturally
- Place the tape measure at the base of the neck (where it meets the shoulders)
- Run the tape along the spine to the base of the tail (not to the tip)
- Keep the tape in contact with the dog's back (don't pull it tight through the air)
- Record measurement in centimeters
Note: Most general harnesses don't require body length. This is mainly for breed-specific harnesses or long-backed breeds.
The Two-Finger Rule Explained:
When measuring, the tape should be snug enough that it won't slide around, but loose enough that you can comfortably slide two fingers between the tape and your dog's body. This is the same tightness your harness should be when fitted. Too tight and you'll order a size too small; too loose and you'll order a size too large.
Recording and Using Your Measurements
Write Everything Down Immediately
Record your measurements like this:
Example Measurement Record:
- Dog's Name: Max
- Breed: Cocker Spaniel
- Weight: 14kg
- Chest Girth: 52cm
- Neck Circumference: 38cm
- Body Length: 45cm (if measured)
- Date Measured: 13 January 2026
Comparing to Size Charts
Once you have your measurements, compare them to the harness manufacturer's size chart:
- Chest girth is king: This is the primary sizing metric
- Check neck fits within range: Ensure neck measurement also falls within the size range
- Weight is secondary: Use it as a sanity check only
- Between sizes? Read on...
What If My Dog is Between Sizes?
If your measurements fall between two sizes, here's how to decide:
| Scenario | Size Up If... | Size Down If... |
|---|---|---|
| Build | Broad chest, stocky, muscular | Lean, narrow, slim build |
| Coat | Thick, fluffy, double coat | Short, smooth, thin coat |
| Age | Puppy still growing | Senior, not changing size |
| Adjustability | Harness has less adjustment range | Harness is highly adjustable (4+ points) |
| Weight trend | Likely to gain weight (puppy, underweight) | On weight loss plan |
General Rule: When in doubt, size up. Most harnesses have 5-10cm of adjustment room. It's better to have a slightly large harness you can tighten than a too-small harness you can't loosen beyond maximum adjustment.
Breed-Specific Measuring Tips
Different breeds have unique body shapes that affect how you measure and size harnesses:
Brachycephalic Breeds (Pugs, French Bulldogs, Bulldogs)
- Challenge: Barrel chest, thick neck, breathing issues
- Measuring tip: Chest measurement is significantly larger than weight suggests
- Sizing advice: Prioritize chest girth over weight. Ensure breathable materials.
- Special note: Measure carefully around neck folds - tape can get caught in wrinkles
→ Complete Pug Harness Guide | → Complete French Bulldog Harness Guide
Long-Backed Breeds (Dachshunds, Corgis, Basset Hounds)
- Challenge: Short legs, long spine, prone to back problems
- Measuring tip: Body length measurement is essential
- Sizing advice: Look for harnesses specifically designed for long backs
- Special note: Harness should not extend past the last rib to avoid spine pressure
→ Complete Dachshund Harness Guide
Deep-Chested Breeds (Labradors, Golden Retrievers, Spaniels)
- Challenge: Broad, deep ribcage
- Measuring tip: Make sure tape is at the very widest point (further back than you think)
- Sizing advice: Chest girth measurement might put you in a larger size than weight suggests
- Special note: Check that girth strap sits behind legs, not in armpits
→ Complete Labrador Harness Guide | → Complete Spaniel Harness Guide
Small/Toy Breeds (Chihuahuas, Yorkies, Pomeranians)
- Challenge: Tiny, delicate, can be wiggly during measuring
- Measuring tip: Use extra treats to keep them still. Consider measuring on a table (with helper for safety)
- Sizing advice: Lightweight harness essential - heavy harnesses overwhelm tiny dogs
- Special note: Escape artists - make sure sizing is snug enough they can't back out
Crossbreeds (Cockapoos, Labradoodles, Cavapoos)
- Challenge: Unpredictable build, thick/curly coats
- Measuring tip: Measure through the coat to the skin if coat is very thick
- Sizing advice: May need to size up for coat volume
- Special note: Harness should work even when coat is wet and compressed
Common Measuring Mistakes (And How to Avoid Them)
Mistake #1: Measuring Over a Thick Coat
The Problem: Measuring over fluffy coats adds 2-5cm of inaccurate fluff
The Fix: Compress the coat slightly when measuring. The tape should be against the body with minimal coat interference. Think about how compressed the coat will be under an actual harness.
Mistake #2: Measuring Too Close to the Front Legs
The Problem: The narrowest point (just behind legs) gives an inaccurately small measurement
The Fix: Measure at the widest part of the ribcage - typically 5-8cm behind where the legs attach. This is where the harness actually sits.
Mistake #3: Letting Your Dog Sit or Lie Down
The Problem: Chest expands differently when sitting/lying, giving wrong measurement
The Fix: Always measure with your dog standing naturally on all four paws. Use treats to encourage standing position.
Mistake #4: Pulling the Tape Too Tight
The Problem: Tight tape compresses the body, giving a measurement that's too small
The Fix: Use the two-finger rule. The tape should be snug but not compressing the ribcage. Remember, this is how tight the harness will be.
Mistake #5: Measuring After Meals
The Problem: Full stomach bloats the chest area artificially
The Fix: Measure before meals or at least 2 hours after eating when stomach is normal size.
Mistake #6: Only Measuring Once
The Problem: Easy to misread tape or have dog move during measuring
The Fix: Always measure at least twice. If measurements differ by more than 1-2cm, measure a third time. Use the average or most common measurement.
Mistake #7: Using Metal Tape Measures
The Problem: Rigid, cold, uncomfortable, can pinch or scratch
The Fix: Always use soft fabric tape measures. They're £2-5 at any craft shop and infinitely more accurate for dogs.
Mistake #8: Relying on Weight Alone
The Problem: Weight doesn't account for body shape, build, or coat thickness
The Fix: Always measure. Weight is a secondary guide only.
The Most Expensive Mistake: Not measuring at all and guessing based on breed or weight. This results in returns (£3-5 postage each way), delays, and potentially using an ill-fitting harness that causes injury. 5 minutes measuring saves weeks of hassle.
Measuring Puppies for Harnesses
Puppies present unique challenges because they're growing constantly:
How Often to Re-Measure Puppies
- 8-16 weeks: Every 2 weeks (rapid growth phase)
- 4-6 months: Monthly
- 6-12 months: Every 6-8 weeks
- After 12 months: Most breeds are close to adult size
Sizing Strategy for Puppies
- Choose adjustable harnesses: Look for maximum adjustment points (4+)
- Size for current measurements: Don't try to buy one size up "for growth" - it won't fit properly now
- Budget for 2-3 harnesses: Most puppies need sizing up twice before adult size
- Measure weekly: Check fit weekly and adjust straps as needed
Puppy Growth Tip: When your puppy's measurements reach the top 20% of their current harness size range, it's time to order the next size up. Don't wait until they've outgrown it completely - order proactively so the new harness arrives before the current one is too small.
→ Complete Puppy Harness Guide UK
Shop Adjustable Puppy Harnesses →
After You Receive Your Harness: Checking the Fit
Measurements are only half the story. Once the harness arrives, you need to check actual fit:
The Complete Fit Checklist
Visual Check (Before Walking):
- Chest plate position: Sits on breastbone, not near throat
- Girth strap placement: Behind front legs, not in armpits
- Centered positioning: Harness sits evenly on both sides
- No gap at shoulders: Straps should follow body contours
- Two-finger rule everywhere: Can fit two fingers under all straps
Movement Check (Walk Around House):
- No rotation: Harness stays centered as dog moves
- No rubbing: Check under arms and behind legs
- Full range of motion: Dog can sit, lie down, walk normally
- No restriction: Breathing sounds normal, no gagging/coughing
First Walk Check (After 5-10 Minutes):
- Still centered? Hasn't shifted to one side
- Any red marks? Check for rubbing spots
- Dog comfortable? Not scratching at it or acting bothered
- Still secure? Dog can't back out or slip free
Red Flags That Mean Wrong Size:
- Chest plate rides up toward throat
- Straps sit in armpits rather than behind legs
- Harness rotates 90+ degrees during walking
- You can fit whole hand under straps (too loose)
- Can't fit two fingers under straps (too tight)
- Dog can back out despite adjustments
- Red marks or hair loss after one walk
If you see these signs, you likely need a different size even if measurements suggested otherwise. Contact the manufacturer for sizing advice before continuing use.
General UK Dog Harness Size Chart
This is a general guide. Always check specific manufacturer size charts as they vary:
| Size | Chest Girth | Neck Circumference | Typical Weight | Example Breeds |
|---|---|---|---|---|
| XS | 30-40cm | 20-30cm | 1-4kg | Chihuahua, Yorkie, Toy Poodle, Puppy |
| Small | 38-50cm | 28-38cm | 4-10kg | Pug, Shih Tzu, Miniature Dachshund, Small Cockapoo |
| Medium | 48-60cm | 35-45cm | 9-16kg | Cocker Spaniel, French Bulldog, Medium Cockapoo, Beagle |
| Large | 56-70cm | 42-52cm | 15-30kg | Labrador, Springer Spaniel, Border Collie, Bulldog |
| XL | 66-80cm | 48-60cm | 25-40kg | Large Labrador, Rottweiler, German Shepherd |
Note: These measurements overlap because different manufacturers use different ranges. Always refer to specific product size charts.
Shop All Dog Harnesses →Breed-Specific Harness Guides
- Best Harness for Labradors UK
- Best Harness for Cockapoos UK
- Best Harness for All Spaniel Breeds UK
- Best Harness for Small Breeds UK
- Best Harness for French Bulldogs UK
- Best Harness for Pugs UK
- Best Puppy Harness Guide UK
Related Harness Guides
Frequently Asked Questions
What measurements do I need to buy a dog harness?
You need three key measurements: chest girth (the most important - measured around the widest part of the ribcage just behind the front legs), neck circumference (measured at the base of the neck where a collar sits), and optionally body length (from base of neck to base of tail). Always measure in centimeters for UK harness sizing. Use a soft fabric tape measure and ensure your dog is standing naturally.
How do I measure my dog's chest for a harness?
Stand your dog naturally on all four legs. Place a soft tape measure around the widest part of their ribcage, just behind the front legs where the harness will sit. The tape should be snug but not tight - you should fit two fingers under it comfortably. Record the measurement in centimeters. This is your dog's chest girth and the most important measurement for harness sizing.
Should I size up or down if my dog is between sizes?
If your dog's measurements fall between two sizes, size up if they have a broad chest, thick coat, or are still growing (puppies). Size down only if they have a narrow build and the larger size would be excessively loose. Most adjustable harnesses accommodate 5-10cm variation, so the size up usually provides better fit with room to adjust. When in doubt, size up - you can tighten straps but can't loosen beyond maximum adjustment.
How tight should a dog harness be?
A properly fitted harness should follow the two-finger rule: you should be able to fit two fingers comfortably (but snugly) under any strap. Too tight restricts breathing and movement; too loose allows escape and causes rubbing. The harness should stay centered when your dog moves, not rotate or slide. Check fit after the first walk and readjust as needed.
Do I measure my dog for a harness differently than for a collar?
Yes, harness and collar measurements are different. Collar sizing uses neck circumference only. Harness sizing requires chest girth (most important), neck circumference, and sometimes body length. The chest measurement is taken around the widest part of the ribcage behind the front legs, not around the neck. Always follow the specific measurement instructions for harnesses rather than using collar measurements.
Final Thoughts: 5 Minutes of Measuring = Years of Perfect Fit
Measuring your dog properly takes 5 minutes. Getting it wrong costs time, money, and potentially your dog's safety.
Quick Recap:
- Get a soft fabric tape measure
- Measure chest girth at widest point (most important)
- Measure neck circumference at base
- Measure body length if required
- Use the two-finger rule (snug but not tight)
- Record measurements in centimeters
- Compare to manufacturer size chart
- When in doubt, size up
Your dog will wear their harness hundreds of times. Make sure it fits properly from day one.
Shop Dog Harnesses (All Sizes) →
