What this unit was
Megalithic yard (Thom hypothesis) is modelled here as a length standard of the Druid tradition, associated with Britain and Brittany during Neolithic and Early Bronze Age hypothesis. The converter represents one MY as 0.829 m; its basis is statistical-hypothesis. The matrix carries an indicative uncertainty of ± 0.03 m.
Within that setting, the unit belonged to a working system for survey, building, travel, and the organisation of built space. It should be read with its period, locality, and evidential basis attached, not as a universal value shared by every culture using a similar name.
Evidence of use and sources
The working value is traceable to Thom 1977 The Megalithic Yard. Its record is classified as low confidence and uses the stated basis rather than an assumed culture-wide constant.
Local-library boundary. The supplied local library has no directly pertinent quotation for this tradition. The linked record source supports the stated conversion; three relevant local quotations require a dedicated source acquisition.
What the unit meant
Engineer Alexander Thom argued that British and Breton megalith builders used a common unit of about 2.72 feet or 0.829 m. His case came from statistical clustering in surveyed circle diameters rather than a marked rod, text, or inscription. The proposal became central to debates about prehistoric geometry, astronomy, and the organisation required to transmit a standard.
How this site models it
The converter includes Thom’s 0.829 m value so readers can reproduce the hypothesis against Stonehenge and other plans. It is labelled interpretive reconstruction, given low confidence, and assigned a broad plus or minus 0.03 m uncertainty. That treatment preserves the mathematical question without promoting the unit to measured historical fact.
What not to infer
Later statistical work found that much of the apparent signal may reside in selected regional subsets, especially Scottish data, and archaeologists have questioned site identification, survey error, chronology, and circular selection. A match in megalithic yards is therefore a result to investigate, not proof that builders carried one standard rod across prehistoric Britain.
Stonehenge: the case-study lens
The world’s best-known prehistoric stone circle combines strong solar geometry with the enduring and disputed claim that megalith builders shared a standard yard. This pairing is a historically bounded investigation, not a claim that one decimal unlocks the whole building.
Open the full Stonehenge dossier.
Values in the site matrix
| Standard | Representative | Uncertainty | Region | Period | Confidence |
|---|---|---|---|---|---|
| Megalithic yard (Thom hypothesis) | 0.829 m | ±0.03 m | Britain and Brittany | Neolithic and Early Bronze Age hypothesis | low |
Sources
- Thom 1977 The Megalithic Yard; basis: statistical hypothesis.