For decades in the United States, the most common go-to beginner horn mouthpieces have had very small inner diameters. These mouthpieces have worked quite well for many students with narrower lips, offering them an efficient introduction to the instrument. For students with fuller lips, however, these small mouthpieces do not always work as well. There are other cost-effective options that will work better for a greater number of people. Students and teachers do not have to be limited in this regard. Educators can facilitate our instruction to fit each individual student’s needs so that they are enabled to sound their very best.

The Inner Diameter

The inner diameter of a mouthpiece is the measurement of the open space across the top of a  mouthpiece from inside edge to edge of the rim. Horn mouthpieces span from roughly 16 to 19 millimeters in inner diameter, with historic or custom mouthpieces sometimes manufactured outside of these measurements. 

At close to 16 millimeters, most beginner mouthpieces are among the smallest horn mouthpieces in production. These diminutive rims often result in the mouthpiece having to sit on some of the flesh of the lips for students with medium or fuller lip sizes, restricting the vibrating surface of the embouchure and possibly creating problems in embouchure formation, tone production, range development, dynamic contrast, and flexibility. 

Many students may have to set the entire bottom portion of the rim into the flesh of the lower lip for these small mouthpieces. To be clear, this can work well as a setting for some students, but it will not be functional for everyone. Ideally, and according to the facial structure of the teeth, lips, jaw, etc., the student should have the option of setting the rim against the lower lip without being forced to set into the lower lip due to the limiting inner diameter of the mouthpiece. Another problem that can often develop from a student trying to make a small mouthpiece work when it doesn’t is the sliding down of the rim below the upper edge of the flesh of the top lip, pinning the upper lip with the rim of the mouthpiece and inhibiting aperture vibration. As with all possible formations of an embouchure, some might have success with this configuration, but many students will be inhibited in all aspects of playing without the ability of the top lip to vibrate freely below the upper area of the rim.  

There are mouthpieces made with larger inner diameters that can help students avoid these dilemmas. Similar to many other concepts in brass pedagogy, the surest path to success on the instrument could look very different in embouchure setup for each student. I advise teachers to help their students find what works for them, even if it is not what has been prescribed in texts or in mainstream pedagogy. This kind of approach is student-centered; not method or teacher-centered. We can – and should – adapt our approach to be flexible to help each student. This is why we must consider mouthpieces that better meet the needs of all of our students.

Middle Ground

With the 16-19mm spectrum of mouthpieces available, the middle option is roughly 17.5mm in diameter. This measurement works well for most students. It may feel slightly large for players with narrower lips, but even they can benefit from the option of being able to put the flesh of their lips entirely inside the rim. Even for smaller lips, 17.5mm may not feel impractically large. Due to the need for freedom in the vibration of the aperture for effective sound production, the possible issues caused by too wide of an inner diameter present, perhaps, far less of a hindrance in sound production than issues caused by too small of an inner diameter for most players. 

These differences to within one to three millimeters may seem like an insignificant and imperceptible span of distance, but our lips are actually incredibly sensitive to these measurements. One millimeter difference can feel like half an inch! My students have seen the immediate difference in response, sound, and range with a change of inner diameter; for better and for worse. This has been my own personal experience as well.


It is important to note that there is no fixed rule among professionals. Some virtuoso players with less-full lips play large inner diameters. Some virtuosos with full lips play small inner diameters. These choices have much to do with their approach, facial/dental structure, embouchure setup, and playing philosophy/goals. For most beginners, however, a medium-sized mouthpiece will work best until they can decide/experiment to find what works better for them. 

Teachers should also be aware that students may need to change mouthpieces as their body grows, their playing ability develops, or as they acquire braces on their teeth. Additionally, they may discover they need a different mouthpiece in their own practice or in work with a private teacher or band director one-on-one.

Unfortunately, the measurement of inner diameter is not precisely uniform across all makers. Where they take this measurement may be inconsistent. Due to wear and tear on tools and other imperfections, mouthpiece making is not an exact science. Any recognizable company’s measurement near 17.5mm will, nonetheless, be near the midpoint of the range of inner diameters.


In the interest of good faith, impartiality, and fairness to the many companies offering mouthpieces to the public, I do not wish to recommend specific brands and models here. In 2023, quality horn mouthpieces that I believe could be considered to be “affordable” for students cost roughly between $40 and $100. Custom mouthpieces can run into hundreds of dollars, so finding an inexpensive option is important to keep the instrument accessible for all students and band programs across the socio-economic spectrum. For the advancing student who really wants to find a perfect fit regardless of the cost, going to a horn workshop or a retail horn shop where they can try different models in person would be a great way to explore the parameters of mouthpiece design.

Ideally, a private teacher or band director could be accommodating for their students by owning several mouthpieces from across the spectrum of sizes to allow students to select what feels comfortable to them. This might include a mix of three to five mouthpieces of roughly the following size options from smaller to larger: 16.21mm; 17mm; 17.25mm; 17.5mm; 18mm. 

For larger diameters than these, the price tends to go up quite a bit. These sizes are typically only found among custom makers. I would like to see the well-known and less-expensive mouthpiece manufacturers offer a student mouthpiece in the 19mm size someday. Interestingly, some of the largest European-made mouthpieces listed as 18mm to 18.5mm feel much larger than any of the widest American-made mouthpieces. These are very likely 19mm or larger based upon the measurement points used by American companies. Some of these options are affordable and are sold by American retailers, which can help with shipping costs and lower wait times than shipping from Europe. 

In addition to a moderate rim inner diameter, it is important for beginner mouthpieces to fall in the medium range of rim surface area and shape, bore size, and cup depth characteristics. Moderating mouthpiece specifications is helpful in avoiding bad habits that can creep in as beginners try to manage extremes in equipment design. 

Most manufacturers publish a set of charts with individual dimensions of their offerings for customers to compare. Although it can be confusing to locate the inner diameter listings for each company, they will usually refer to this measurement as the “inner diameter”, “cup diameter”, “cup diameter inside”, “rim inner diameter”, or something along those lines and in reference to millimeters in measurement. 

Note: Some of the less well-known mouthpiece brands for sale on eBay or Amazon are enticingly low in price but should be avoided. Some have extreme inner diameters of 16mm and bore sizes that are nearly unusably small. It is best to go with a recognized company for consistency of production, uniformity in meeting the needs of the profession, and quality of design/materials. 

The good news for the horn teacher, band director, or student is that there are options! One does not have to be limited by their mouthpiece. Teachers can help set all of their students up for success by starting them on a true mid-sized mouthpiece or by giving them options to find what will work best for them. 

Best wishes in all of your teaching endeavors!