Museum accession number format, explained with examples

What each part of the number means

The first part is the year the accession was received, written in full. Guidance from the Collections Trust asks for the full four digit year and for the year to come first, so that numbers sort in the order things arrived and 1998 is never confused with 2098. The Saskatchewan museums tip sheet says the same: always the full year, never a shortened one.

The second part counts accessions within that year: the first gift, purchase or bequest of the year is 1, the next is 2. One accession is one acquisition from one source at one time, however many objects it holds. The third part counts the objects inside that accession, from 1.

Letters are for pieces that make one object: a pair of gloves, a teapot and its lid, a box and its cover. The Oklahoma Museums Association module keeps letter suffixes to exactly those cases; the pieces of a set that do not physically go together, such as the spoons of a flatware set, each get their own object number instead.

The choices a museum makes, and keeps

Separators, padding and how parts are written are a house style. What matters is that every number is unique and that the museum keeps to one style. The table in the worked example shows the same number written the common ways. Guidance differs on padding: the Collections Trust advises against leading zeros (2026.5, not 2026.05), while many North American guides pad to three places (2015.001.010). Both work; mixing them in one collection is what causes trouble, because 2026.14 and 2026.014 are the same number to a person but not to a spreadsheet sort.

If the collection already has a consistent system, keep it. Renumbering objects that are already marked is slow, risks losing the link between an object and its papers, and is discouraged by the Collections Trust unless numbers actually clash. Older numbers written another way, such as a two digit year, can stay as they are marked.

Gaps and duplicates

A number, once given, is never reused, even if the accession is later declined or deaccessioned. A gap in the sequence is not an error, but it should be explained: a note in the register saying why 2025.3 was never used saves a future volunteer from searching the store room for it. A duplicate, two objects carrying the same number, is an error and one of them must be renumbered with a note.

Worked example: the same number in each style, and the demo's number check

In the demo catalogue of the Millbrook Valley Historical Society (an invented society with 7 accessions and 11 objects), the number check lists these gaps: 1998.1 to 1998.11, 2025.3. The first is the old 1998 series, where only one accession has been entered so far; the second is a number set aside for a gift that was declined, which the register explains. The next accession number for 2026 is 2026.2.

The demo's oldest accession is written 98.12, the two digit way; the engine reads it as 1998.12 and lists it as written another way, without changing it. A two digit year up to 40 is read as 20xx and above it as 19xx. The teapot with its lid is 2024.1.2a-b. After the 26th part (z), letters continue aa, ab; some museums prefer aa, bb, and either works if it is used every time.

Common mistakes

• Using a two digit year for new numbers. Write 2026, not 26.
• Giving the pieces of a set letters instead of their own object numbers, or giving a lid its own object number instead of a letter.
• Reusing the number of a declined or deaccessioned accession.
• Padding some numbers and not others, so 2026.9 sorts after 2026.10 in a spreadsheet and duplicates such as 2026.14 and 2026.014 go unnoticed.
• Renumbering a whole collection to a new style when the old numbers are consistent and already marked on the objects.

Do it in the catalogue

Open the catalogue to number an accession and its objects, add photos and locations, and print the register, labels and receipts. Everything stays in this browser; nothing is uploaded and there is no account. Save the catalogue file after every session.

Sources

Last reviewed 28 September 2026 against:

• Numbering, Collections Trust, guidance updated August 2024, read 28 September 2026. Used for: Year based accession numbers with a running sequence and a further part for each object, full four digit years first, full stops as separators, no leading zeros, entry and temporary numbers attached reversibly, and renumbering discouraged.
• Tip Sheet: How to Label Historic Artifacts, Museums Association of Saskatchewan, 2016 tip sheet, read 28 September 2026. Used for: The three part number with the full year, letter or number suffixes for components, starting a year at its first number, reversible and lightfast marking materials, paper tags for unstable objects, and never tape.
• Module 26: Numbering Systems, Oklahoma Museums Association, read 28 September 2026. Used for: Keeping a consistent existing system, the three number system for a new one, letter suffixes only for pairs and pieces that fit together, and separate numbers for the pieces of a set.

This guide is our own summary, not a rule book. Rules are paraphrased, never quoted at length, and if this page disagrees with the current published rules, the rules win. Curatorbook is not affiliated with, endorsed by, or connected to any museum, association, standards body or software vendor, including the Collections Trust (Spectrum), the American Alliance of Museums, the American Association for State and Local History, the National Park Service, PastPerfect, CatalogIt, MUSARCH, CollectiveAccess and Omeka.