Dog Collar Size Guide | Measure Once, Fit Right

One wrong measurement and that “perfect” collar sits too loose at dinner or too tight after a run. The real fix is a thirty-second check with a piece of string. This guide walks through every measurement method, the exact calculation for each collar type, and the size chart that matches most US brands — so the collar you order is the one that stays on.

Measuring Your Dog’s Neck: Three Reliable Ways

All three methods start at the same spot: the base of the neck, right above the shoulders, where the collar naturally sits. Pick whichever tool you have on hand.

Method 1: String or Phone Charger Cable

This works when you don’t own a sewing tape measure. Wrap a piece of string or a phone charging cable around the thickest part of the dog’s neck. Pull it snug enough that you can fit two fingers between the string and the neck — no tighter, no looser. Mark where the end meets the string, then lay it flat against a rigid ruler to read the length.

Method 2: Current Collar (But Avoid the Common Mistake)

Take off the collar the dog currently wears. Lay it flat without stretching it. Measure from the center of the buckle to the hole you currently use. The critical mistake: measuring end-to-end (buckle tip to last hole) adds one to two inches, which pushes you into the wrong size.

Method 3: Soft Tape Measure

A fabric sewing tape measure is the most direct route. Wrap it around the neck at the same base-of-neck position. Pull it snug but not tight — the same two-finger gap applies. Read the number where the tape overlaps, and write it down.

How Collar Sizing Calculations Change by Collar Type

Not all collars use the same math. The measurement you just took is the starting point, not the final number.

• Neck-sized collars (NS): The dog’s neck measurement is the collar size. A 16-inch neck takes a 16-inch collar.
• Collar-sized collars (CS): Add 4-5 inches to the neck measurement. A 16-inch neck means a 20- or 21-inch collar.
• Metal buckle (open-end) collars: Round the neck measurement down to the nearest even number. A 19-inch neck calls for an 18-21 inch collar.
• Quick-release adjustable collars: The neck measurement must fall within the stated adjustable range. A 13-inch neck needs an 11-16 inch adjustable collar, not a 16-20.
• Slip (choke) collars: Measure the widest part of the dog’s head — just in front of the ears — not the neck.
• Martingale collars: Follow the brand’s specific guide, because these are intentionally looser when relaxed.

The table below shows the standard US size ranges that most brands follow. Your measurement should land near the middle of the range to leave room for seasonal fur changes or a few extra pounds.

The Two-Finger Rule and Other Safety Checks

The collar passes the safety test if you can slide two fingers between the collar and the dog’s neck without forcing them. A collar that fits tighter can restrict breathing or cause coughing during walks. A collar that fits looser than two fingers can slip over the dog’s head — especially on breeds with narrow skulls like Greyhounds or Whippets. Once buckled, test it: the collar should rotate freely around the neck but never slide over the widest part of the head.

If your dog is still a puppy, buy an adjustable collar and check the fit monthly. Most breeds outgrow their current size within one to two growth spurts. If your grown dog lands between two sizes on the chart, pick the smaller size so there is less excess strap material sticking out past the buckle.

Special Cases: Hindquarters Collars and Deep-Chested Breeds

A standard neck collar sits above the shoulders. Hindquarters collars, sometimes called back or body harnesses, wrap around the widest part of the ribcage just behind the front legs. Brands like Hindquarters and Long Paws sell these in a separate size range starting at XS (7 to 12 inches) through Large (16.5 to 26 inches). Measure at the circumference behind the shoulders, not at the neck. Deep-chested breeds like Bulldogs often need a larger hindquarters range than their neck measurement suggests.

For a full rundown of collars built to fit that broad chest and short neck profile, check our tested roundup of the best collars for bulldogs — each one was measured and walked in before making the list.

When the Collar Arrives: The Final Fit Test

Before the first walk, run through this quick checklist. The collar should sit high on the neck, right behind the ears and above the shoulders. Confirm the two-finger gap exists on both sides of the neck. Tug the collar forward toward the dog’s nose — it should stop at the widest part of the head, not slip over the ears. If it passes those three checks, the size is right.

For quick-release collars, snap and unsnap the buckle three times to make sure the plastic isn’t stiff or cracked. Leather collars will stretch slightly over the first month, so start on the tightest comfortable hole and tighten the buckle by one hole every two weeks as the leather relaxes.