Mozart Köchel Numbers, Explained Simply

The number identifies the work, not its difficulty

A Köchel number is a catalog identifier for a composition associated with Wolfgang Amadé Mozart. It usually appears as K., K, or KV followed by a number: for example, KV 525. The letters refer to Ludwig von Köchel, whose chronological and thematic catalog first appeared in 1862. They do not describe key, movement count, quality, or the number of powdered wigs required for entry.

Use the number to distinguish works that share generic titles such as “Piano Sonata” or “Symphony.” Then confirm the title, key, scoring, and catalog edition, especially when comparing older books and recordings.

Why titles alone are not enough

Classical work titles frequently describe a form and performing forces rather than provide a unique name. “Piano Concerto No. 20” is helpful, but its numbering belongs to a modern sequence and may be displayed differently across catalogs. A Köchel identifier narrows the search more reliably.

Nicknames create another layer. Some are familiar and convenient, but a nickname can be later, informal, translated, or shared. Search with both the displayed title and KV number. When the result gives a different key or ensemble, pause: you may have found a recording bundled under an album title rather than the intended work.

The Catalog Desk covers other ways to match recordings, scores, and sources.

Why one composition can show more than one number

The Köchel catalog did not freeze in 1862. Scholarship changed dates, authenticity judgments, relationships among sketches and works, and the organization of the catalog. Major revisions appeared in 1905, 1937, 1964, and 2024. Older sources may therefore use alternate forms such as a number with a letter, a number in parentheses, or a reference tied to a particular edition.

The International Mozarteum Foundation's official Köchel Catalog Online reflects the 2024 revision. Its account of the revision explains that the new edition returns authentic works to the earliest number they had in the catalog's main body. It also assigns 95 new numbers beginning with KV 627 to compositions that had not previously received a main-body number.

That means a higher number is not automatically a later composition. The original scheme aimed at chronology, but discoveries and reassessments complicate the sequence. Read KV as an identifier with historical structure, not a flawless timestamp wearing a waistcoat.

How to read a catalog entry

Start with five fields:

1. Identifier: the KV number used by the current entry.
2. Title or opening words: generic title, nickname, or text incipit.
3. Key: useful for distinguishing works with similar titles.
4. Scoring: the voices or instruments required.
5. Date and status: composition evidence and whether the item is complete, fragmentary, lost, doubtful, or misattributed.

Status matters. A catalog can document uncertainty; inclusion in a historical appendix is not the same thing as secure authorship. Do not convert “attributed to” into “by” because a playlist field lacks patience.

For research, the official catalog's core data can lead into the Digital Mozart Edition work search, where searches can use a Köchel number or title. Check the editorial information attached to a score rather than assuming every free scan represents the same text.

Use the number when comparing recordings

Search a streaming service, library catalog, shop, or concert archive with the composer's name, KV number, and movement marking. For example:

Mozart KV 525 Allegro

Then verify that the album track belongs to the correct work. Multi-work recordings and abbreviated mobile displays can hide the key or full title. Movement order also matters: an individual track is not necessarily the entire composition.

The number does not identify one definitive performance. Ensembles may use different editions, instruments, ensemble sizes, repeats, tempos, cadenzas, or completions. Those differences are reasons to compare, not evidence that one search result is broken.

The guide to listening to a Mozart symphony offers a simple method for comparing two interpretations without turning the evening into a spreadsheet emergency.

Cite the version you actually used

When writing program notes or coursework, record the current catalog identifier, work title, key, and movement. Name the score edition or recording separately. If an older source supplies another number, preserve it as an alternate rather than silently “correcting” the historical quotation.

Finally, recheck the official catalog when attribution or numbering is central to the claim. Catalogs are scholarly tools, and scholarship moves. The tiny letters beside a Mozart title do not replace listening—but they are excellent at ensuring everyone has pressed play on the same piece.