Plural of “datum”

The plural of datum is data.

Why

"Datum" is Latin for "a given thing," the neuter past participle of "dare" (to give), and it kept the standard Latin neuter second-declension plural pattern, -um becoming -a, exactly as in "medium/media" and "bacterium/bacteria."

In practice, "datum" has almost vanished from everyday English, surviving mainly in surveying and specialized technical writing (a "geodetic datum" as a fixed reference point), while "data" itself has undergone a genuine and much-debated shift: it's now overwhelmingly treated as a singular mass noun in everyday and even much scientific writing ("the data is clear") rather than as a true countable plural ("the data are clear"), a live grammatical change many style guides have only recently started accepting. Surveying and geodesy are probably the last fields where an English speaker will still regularly encounter the true singular "datum" in ordinary technical conversation, referring to a fixed reference point or level from which measurements are calculated (a "vertical datum" for elevation, a "horizontal datum" for mapping coordinates), a specialized survival of the word's original Latin singular sense that has almost entirely disappeared everywhere else in English. This narrow technical persistence is part of why so many English speakers today are surprised to learn "datum" exists at all as a distinct singular form separate from "data."

Usage note

Formal scientific and academic style guides, especially in statistics and research methodology, still often insist on treating "data" as a plural requiring "are" and "these," while general news writing, technology journalism, and most everyday usage now treat it as a singular mass noun requiring "is" and "this" — meaning a writer's choice here genuinely depends on the register and publication they're writing for, not on a single settled rule.

The Associated Press Stylebook shifted its own guidance on "data" toward accepting singular treatment in general-audience writing, a change that reflects how thoroughly the word has been reanalyzed by ordinary speakers as a singular mass noun like "information," even as academic style guides in the sciences continue to hold the older plural line for now. Style guides in computing and technology journalism have moved the fastest toward treating "data" as fully singular, likely because software and technology writing rarely needs to distinguish individual countable data points from data considered as an aggregate mass, the same way "information" or "knowledge" never needed a plural in ordinary usage either.

Common real mistakes

There isn't a clean single "correct" usage anymore, which is itself the main point of confusion — writers moving between academic and general contexts often get corrected in both directions, told to switch from singular to plural treatment in one publication and the reverse in another, reflecting real disagreement among style authorities rather than a stable rule any writer is simply failing to apply. A further wrinkle worth flagging: some writers now avoid "datum" altogether even in its narrow surveying sense, substituting phrases like "reference point" specifically because the singular Latin form has become so unfamiliar that it risks confusing a general audience.

The wider pattern

The same Latin neuter -um/-a plural governs "medium/media," "bacterium/bacteria," "curriculum/curricula," and "memorandum/memoranda" — a family where, unlike "datum/data," most members have kept a genuinely functioning singular form still in active everyday use, making "datum" unusual for how nearly extinct its own singular has become outside specialist technical writing.

Examples

• The surveyor referenced a fixed datum point on the coastal map.
• The data show a clear increase in enrollment this year.
• This data is the most reliable we've collected so far.
• Researchers compared each datum against the historical baseline.
• The new data suggest a different explanation entirely.
• Every datum in the spreadsheet was double-checked for accuracy.
• The report's data has been peer-reviewed twice.
• A single unreliable datum skewed the entire early analysis.
• The team gathered data over eighteen months of fieldwork.
• These data were collected using three separate instruments.
• The new geodetic datum improved the accuracy of coastal elevation maps.
• Analysts warned that incomplete data could skew the entire forecast.
• Only one datum in the entire dataset fell outside the expected range.