Incorrect Sizing Methods
Using Only Length & Circumference
For example, these two muzzles pictured are the same length and circumference. Are they the same shape in the slightest? No! Two completely different dogs would wear these muzzles. One width is 3” the other 5”. One height is 5.5” the other closer to 4.5”. There is absolutely no way to correctly size with only these measurements.
To prove this, please tell me which of these muzzles is the widest and which is the tallest:
4" x 12"
3"x 13"
4" x 12.5"
I could keep going, but as shown, there is no way to correctly size based on these two measurements on a muzzle, especially when they offer nothing towards the actual shape of the muzzle. Circumference does not show width or closed height, which are more important than length.
Another example would be the CHOPO 18F/69C and 17F/66C. Most company size charts have the same length and circumference but are entirely different muzzles. The 18F with much less height and a longer chin causes it not to fit the dog in everything, including length.
If they had a height measurement, they would have known one would not have worked for their dog before purchasing. The right pic was a bit big for the dog, so they sized down, but the image is a perfect example of why following their measurements helps nothing, especially when we have 6+ on nearly every muzzle.
Who Does It Correctly
MTT has gotten all the essential measurements for you, but many other companies measure their muzzles well. Some are more accurate than others, but it's still better than the two measurements you get from some places.
IF you see the sizing chart mention height, be sure to check if it's front or back height and the shape of the muzzle. Some muzzles are shorter at the front, and they'll measure the height at the back. The width could also be front or back unless specified.
Any other measurements are a bonus, and the more they have, the more accurate the chart will be.
TYDM is a custom company but a great example of how two measurements don't just size dogs.
Most European companies are good at getting more measurements and reasonably accurate too. Chicundscharf is recommended.
Both FDT and DT use more than two measurements, but they are pretty off when measured by MTT properly. We have every size measured anyway, so we shouldn't need their chart. Prestige wire in aus also had their muzzles measured well.
You don't need every measurement as we get, but you still need something to show the height or width of the muzzle; otherwise, it is a complete gamble when purchasing.
Sizing By Yawn Size
Sizing based on your dog yawning is not accurate since this will oversize the fit, you can learn more about this in Measuring Your Dog