The 12-person jury is one of those legal artefacts that has endured through sheer force of repetition, writes Rebecca Ward, MBA.
Why do we have 12 jurors? Not 10, not 15, not an odd number to avoid deadlock. Just 12. The same number as a carton of eggs. The same number as the apostles and the days of Christmas. A dozen strangers, tasked with deciding guilt or innocence, truth or fiction, beyond a reasonable doubt. It’s a question that’s bothered me for years, but the answer, as with so many things in law, comes down to one uncomfortable truth: because we have always done it that way.
The mystical number 12
Twelve is not a number chosen for efficiency or practicality. It was never backed by neuroscience, cognitive load testing, or empirical studies on group deliberation. No, the origin of the 12-person jury is more myth than method.
It harks back to medieval England, where 12 was considered a symbol of completeness and divine order. Twelve months in a year. Twelve tribes of Israel. Twelve apostles. Somewhere between religious symbolism and feudal practicality, English common law settled on 12 “good and lawful men” to decide land disputes. That number stuck, not because it was proven, but because it was familiar.
By the 14th century, 12 had become the gold standard in English felony trials. And when Britain began exporting its legal system to colonies across the world, including Australia, the United States, Canada, and India, it exported that number too. It was part of the legal starter kit: robes, wigs, common law, and a dozen jurors.
The law inherited this mix. We measure in tens, but we judge in twelves. We trade in decimals, but we tell time in sexagesimals. And somewhere between fingers and stars, man decided what mattered, and called it justice.
For all its elegance and utility, 10 was too natural. Too earthly. Ten was the body, fingers, toes, the base of trade and tally sticks. But 12? Twelve was order. Twelve was divine. It mapped the heavens, named the apostles, and gave us the illusion that justice could be cleanly divided like a zodiac chart. In choosing 12, we didn’t just reject 10; we reached for something higher than the human hand could hold.
Unanimity, or bust
In its original form, the jury was designed to reach a unanimous verdict. That made the idea of 12 appealing. It gave weight to the result; a decision reached by 12 people in full agreement felt more trustworthy. The trouble, of course, is that people rarely agree on anything, including guilt.
So why not have an odd number of jurors, say, 11 or 13, to break the tie? The simple answer is that the system didn’t anticipate a tie. If you required unanimity, an odd number didn’t matter. The only acceptable verdict was one all jurors could support.
But that logic has eroded over time. Many jurisdictions now allow majority verdicts. In Australia, majority decisions (typically 11–1 or 10–2) are permitted in criminal trials in most states and territories, including Queensland, NSW, and Western Australia. But we’ve kept the even number. So, mistrials still happen. Hung juries still occur. And everyone still pretends the structure makes sense.
The modern mismatch
Juries today are being asked to absorb complex legal instructions, technical forensic evidence, psychological testimony, and multimedia exhibits, and still reach a “reasonable” conclusion. But we’ve done almost nothing to modernise the group dynamics behind that task.
Twelve people. Locked in a room. No formal training. No whiteboard. No chairperson. No protocols for disagreement beyond sheer will. And we wonder why deadlock is common? We also know that group decision making worsens past about six to eight people. Beyond that point, social conformity increases, dissent decreases, and the loudest voices dominate. In other words, we’ve designed a system that maximises groupthink and called it justice.
Other countries, other numbers
Australia’s own history isn’t uniform either. In NSW, for example, civil jury trials historically used only four jurors, a practice in place until the mid-2000s. The system functioned effectively, suggesting that neither the symbolic weight of 12 nor fears about smaller panels should stand in the way of reform.
Not all jurisdictions cling to 12. Scotland uses 15 jurors and only requires eight to convict. The United States allows as few as six in some civil trials. New Zealand recently reduced the number to 11 in certain cases. Yet the idea of the “classic dozen” persists, particularly in serious criminal trials. Why? Because it’s comforting. Because it’s tradition. Because it looks like justice, even if it doesn’t always function like it.
The oddity of even numbers
From a pure design perspective, even-numbered juries are odd. They introduce the possibility of a 6–6 split. That kind of deadlock leads to hung juries, mistrials, wasted time, and retraumatised victims. An odd number would reduce that risk, and yet we resist it because tradition is a powerful thing even when it stops making sense.
If you were designing a jury system from scratch today, knowing what we know about group psychology, cognitive load, and the impact of trauma, you wouldn’t land on 12. You might choose nine. You might mandate a trained foreperson. You might redesign the room itself. But you wouldn’t replicate what a group of English nobles came up with in the 1300s. And yet, here we are.
At what cost?
The cost of clinging to an outdated model isn’t just inefficiency. It’s injustice. Hung juries mean retrials. Delays. Emotional exhaustion. Public confusion. And, in some cases, guilty people walking free or innocent people left in limbo. The public sees the verdict, or the lack of one, but rarely understands the machinery that produced it. It’s also a system that’s deeply resistant to change. Reforming jury numbers isn’t politically sexy. It doesn’t win votes, and lawyers themselves are often too embedded in the tradition to question it.
Conclusion: Legal by habit, not by reason
The 12-person jury is one of those legal artefacts that has endured through sheer force of repetition. It looks right because we’ve always seen it. But familiarity is not evidence. And tradition is not a defence.
Twelve jurors might once have been symbolic of fairness and balance. But today, in an age of complex evidence, diverse populations, and ever-tightening court resources, it’s worth asking whether the number is still serving justice, or just history. Because when it comes to the courtroom, we should aim for more than rituals in robes; we need a system that works, makes sense, and evolves with reason.
Acknowledgements: With thanks to the Honourable Michael Kirby AC CMG for his input on this article.
Rebecca Ward is an MBA-qualified management consultant with a focus on mental health. She is the managing director of Barrister’s Health, which supports the legal profession through management consulting and psychotherapy. Barristers’ Health was founded in memory of her brother, Steven Ward, LLB.
