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Scientists say everyone should follow '21 second rule' when peeing to stay healthy

Home> News> Health

Published 14:17 3 Feb 2026 GMT

Scientists say everyone should follow '21 second rule' when peeing to stay healthy

Turns out there's more to micturating than you might think

Kit Roberts

Kit Roberts

Experts have advised about a simple rule that everyone should try to follow when they pee.

It's something we do every day, to the point that we probably don't think that anything is wrong unless we notice something new or unpleasant.

Blood or cloudiness is pretty clearly a bad sign, and while strong smells, peeing too often or not enough, are all signs that something might be up. So if there's anything we can do to help keep things normal down there, there is a simple rule we can follow everyday.

It helps you to keep track of your bladder's health, and can be used in addition to keeping tabs on what your urine looks like.

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That's also a useful tool - a dark yellow colour for example might mean you need to drink more water.

But this hack is a different aspect of your peeing, and was put together by mechanical engineering students at Georgia Institute of Technology.

So, what is it?

This rule could help you to monitor your bladder health (krisanapong detraphiphat/Getty)
This rule could help you to monitor your bladder health (krisanapong detraphiphat/Getty)

This is looking at the ideal amount of time that you should be peeing each time you go.

Of course, the students were looking at this from a mechanical engineering perspective rather than a medical one, and if you were worried that something is wrong you should speak to a medical doctor.

Back in 2014, the researchers analyzed how long different sized animals took to empty their bladders.

For creatures that were much smaller, think rats, mice, squirrels and suchlike, their bladder is very small so only takes a fraction of a second.

But animals that weigh more than 3kg, that's around 6.6lbs, the average is around 21 seconds, with the researchers calling the the 'Law of Urination'.

Urine is produced as the kidneys filter out anything unneeded from the blood, with the excess fluid deposited in the bladder.

When the bladder is full, your brain sends signals, then your muscles relax and the wall of the bladder tightens, pushing the pee out of your urethra.

Needing to go too often or not enough could both be bad signs (SimpleImages/Getty)
Needing to go too often or not enough could both be bad signs (SimpleImages/Getty)

But using their observations, the researchers concluded that the duration of peeing is related to gravity as well as the pressure exerted by the bladder contracting, IFL Science explains.

They wrote: "How can bladders of both 0.5 kg and 100 kg be emptied in nearly the same duration? Larger animals have longer urethras, and so greater gravitational force driving flow.

"These long urethras increase the flow rate of larger animals, enabling them to perform the feat of emptying their substantial bladders over approximately the same duration."

The study also gave humans a 'golden rule' for how long is the ideal duration for us be peeing.

Peeing too much or too little could be a sign that something is up, and holding your pee too long could lead to a UTI, kidney disease, or even bladder ruptures.

And if you don't have a stopwatch to hand to time your visit to the smallest room in the house, just sing 'Happy Birthday' at a steady tempo and that should last about 21 seconds.

In case you're overheard, just make sure you share what you've learnt, instead of trying to awkwardly explain away why you sign 'Happy Birthday' as you pee.

Featured Image Credit: Getty Stock

Topics: Health, News, Science, Education, US News

Kit Roberts
Kit Roberts

Kit joined UNILAD in 2023 as a community journalist. They have previously worked for StokeonTrentLive, the Daily Mirror, and the Daily Star.

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