The question might seem basic, but why do juries in the United States consist of 12 members?

Was there an experimental determination of this number?

Would the addition or removal of a juror operate more effectively?


The origin of the jury is a complex mix of Saxon, Danish and Norman custom which morphed and melded along with English Common Law, which is the basis of the law in all ex-British colonies including the USA.

Danish towns in the north and east of England had hereditary “law men”, often 12 in number who decided legal disputes. In parallel the West Saxons (Wessex) in the south and west charged 12 theigns in each area with keeping the peace. When the Normans conquered (who were also of Viking origin) they adopted and adapted the existing legal structures.

In the 12th century, Henry II established that a jury of 12 should decide land disputes. Meanwhile other juries of various sizes were formed to investigate crimes and bring charges - this is the origin of the Grand Juries that still live on in the USA although they have been replaced by a judge in other common law jurisdictions.

Ultimately the jury that brought charges and the jury that decided guilt were split and the size was standardised. However, it is incorrect to say that it is always 12: some jurisdictions have different numbers for different purposes. For example, rule 48 of the US Federal rules for civil procedure sets the number at not less than 6 and not more than 12.

The jury system continues to evolve with various jurisdictions adopting different numbers, majority verdicts and judge only trials.

There is nothing special or “scientific” about 12: it is what it is because it is what it is.

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  • Comments are not for extended discussion; this conversation has been moved to chat. – feetwet Jan 4 '18 at 1:40

It isn't 12, for federal trial courts it's at least 6 and no more than 12. https://www.law.cornell.edu/rules/frcp/rule_48 For grand juries it's more https://www.uscourts.gov/services-forms/jury-service/types-juries. In az it's 6,8, or 12 depending on the matter being considered. https://law.justia.com/codes/arizona/2005/title21/00102.html. I can't go through all the states but it's not always 12.

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Historic tradition mentions a King of the Scotts, Morgan of Glamorgan, as the first to have a jury of 12 to decide on legal cases. His motive, according to tradition, was to take the model of the 12 apostles (the jury) and Jesus (the Judge).

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  • This would be a great answer if you could add a link to a credible source for this "historic tradition." You can edit the answer to do so. I would however note that the number 12 has been popular in ancient pre-Christian cultures, for example in Hebrew scriptures and ancient Greek mythology. It's therefore possible that the link with the 12 apostles was identified after the number 12 was settled on. – phoog Apr 24 '19 at 17:38

The number12 was decided from Jesus 12 apostles who will judge the 12 tribes at judgement day.

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  • It's certainly plausible, but can you back this up with citations of historical research to show that this was actually what the originators of the jury system had in mind? – Nate Eldredge Jan 14 '19 at 5:25
  • In particular, the answer by Dale M traces the custom to Viking invasions of England, and it's not clear to me whether the Vikings were predominantly Christian in that time period. – Nate Eldredge Jan 14 '19 at 5:27

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