Why does Bach use lower numbers for larger mouthpieces?

Historical convention from early 20th century mouthpiece making. Professional sizes came first and got the low numbers. Smaller student sizes developed later and got higher numbers.

Is a Bach 3C better than a Bach 7C?

Neither is objectively better. The 3C has a wider rim that produces a fuller tone. The 7C has a smaller rim that is easier for developing players to manage. Which is better depends on your stage of development and context.

What does the 1.5 mean in Bach 1.5C?

The 1.5 puts the rim diameter between a Bach 1 and a Bach 2 — an intermediate size. Bach introduced it because many orchestral players wanted something between the 1 and the 2.

Can I figure out the mm measurement from the Bach number?

Approximately yes, using a spec table. Published measurements vary slightly between batches. For precise comparisons, measure with a caliper or look up the model in the database.

What's the most popular Bach mouthpiece?

The 7C is the most common by volume — it ships with more student trumpets than any other model. Among adult players, the 3C is very widely used. The 1.5C is the most common orchestral mouthpiece.

Are vintage Bach mouthpieces different from current production?

Bach was acquired by Conn-Selmer; some players report differences between vintage Mount Vernon-era pieces and current production. For most players, current Bach mouthpieces perform at a professional level.

What Do the Numbers and Letters on a Bach Trumpet Mouthpiece Mean?

You picked up a Bach trumpet mouthpiece and it says something like "3C" or "7C" or "1.5B" on the shank. You know those numbers and letters mean something — but nobody has explained clearly what they encode.

This guide does exactly that. By the end you will be able to look at any Bach mouthpiece model name and know what it is telling you about rim size, cup depth, and variants.

The Two-Part Bach Code

Every standard Bach trumpet mouthpiece model name has two parts: a number (rim inner diameter) and a letter (cup depth A through F).

The Number: Rim Inner Diameter

The number refers to the rim inner diameter — the opening at the top of the cup.

The scale runs counterintuitively: lower number = larger diameter.

Bach number	Rim inner diameter	Description
1	~17.00mm	Very large — orchestral specialist
1.5	~16.84mm	Large — orchestral standard
2	~16.76mm	Large-medium
3	~16.76mm	Medium-large — all-around workhorse
5	~16.50mm	Medium
7	~16.20mm	Medium-small — universal beginner
10	~15.90mm	Small — high register specialist
10.5	~15.75mm	Very small — lead/commercial
12	~15.50mm	Very small — high note specialist

Bach 2 and Bach 3 have very similar measurements — most players go from 7 to 5 to 3, skipping the 2 entirely. The jump from 7 to 10.5 is significant — about 0.45mm. Do not jump that far in one step without guidance.

Why lower = larger? Historical convention. Vincent Bach assigned numbers based on early 20th century practice: the lowest numbers were reserved for the largest professional sizes. Smaller student sizes got higher numbers later. There is no deeper logic — it is how it ended up.

The Letter: Cup Depth

A = deepest. F = shallowest. C = standard (the middle).

Bach letter	Cup depth	Tone character	Typical use
A	Deepest	Warmest, darkest	Deep orchestral
B	Very deep	Warm, full	Orchestral, chamber
C	Standard	Balanced	All-around, most common
D	Medium shallow	Brighter, more focused	Jazz mainstream, commercial
E	Shallow	Bright, cutting	Lead trumpet
F	Very shallow	Very bright	High-note specialist

The acoustic reason: A deeper cup creates a larger resonance cavity — warmer, fuller tone. A shallower cup creates a smaller cavity — brighter, more focused tone. This is basic acoustics, not marketing.

What cup depth does NOT do

Cup depth does not give you more high notes. It affects the character and endurance of the notes you already have: shallower cups (E, F) can make it easier to sustain high notes for longer; deeper cups (A, B) make the high register harder to sustain but can improve tone quality when you get there. If you move shallower hoping to gain range, you are misunderstanding what it does. Build range through practice; use cup depth to shape tone.

Putting the Two Together

Bach 7C: medium-small rim, standard cup — universal beginner/intermediate.

Bach 3C: medium-large rim, standard cup — all-around adult workhorse.

Bach 1.5C: large rim, standard cup — orchestral standard.

Bach 3E: medium-large rim, shallow cup — lead configuration.

Bach 10.5C: very small rim, standard cup — high register specialist.

The "W" Suffix

W = wider outer rim. Inner diameter and cup depth match the non-W version; the outer rim is broader for some players' comfort.

The Full Bach Standard Trumpet Line — Decoded

Model	Rim diameter (mm)	Cup depth	Best for
1C	~17.00	Standard	Large bore orchestral
1B	~17.00	Deep	Very dark orchestral
1.5C	~16.84	Standard	Orchestral standard
1.5B	~16.84	Deep	Orchestral warm
2C	~16.76	Standard	Large-medium general
3C	~16.76	Standard	All-around workhorse
3B	~16.76	Deep	Warm jazz / orchestral
3D	~16.76	Medium shallow	Jazz mainstream
3E	~16.76	Shallow	Lead
5C	~16.50	Standard	Medium — middle ground
5B	~16.50	Deep	Warm medium
7C	~16.20	Standard	Beginner / intermediate
7B	~16.20	Deep	Warm medium-small
7D	~16.20	Medium shallow	Brighter small
7E	~16.20	Shallow	Small lead
10.5C	~15.75	Standard	High register / lead
10.5CW	~15.75	Standard	10.5C with wider outer rim
12C	~15.50	Standard	Very small specialist

How Bach Compares to Other Brands

Bach numbers do not translate to Schilke or Yamaha. A Schilke 3 is much smaller than a Bach 3. Yamaha cup letters run opposite to Bach for depth (except C is still roughly "standard").

For cross-brand equivalents, use Equivalent Finder — normalized mm measurements, not brand codes alone.

What to Do Next

Decode any model: Mouthpiece Name Decoder

Browse specs: Mouthpiece database

All major brand systems: Trumpet Mouthpiece Sizes and Numbers Explained

3C vs 7C: Bach 3C vs 7C