How long does it take you to pee? You’ve probably never timed it. But it turns out there’s a specific number that can say quite a bit about your health: 21 seconds. Not 10, not 40 – but 21.
This rule, known as the “The Law of Urination,” was discovered by a group of researchers from the Georgia Institute of Technology after watching hundreds of video clips of animals urinating – including YouTube videos and zoo observations. The law, which earned them the 2015 Ig Nobel Prize in Physics, states that animals weighing more than 3 kilograms (including humans, dogs, and elephants) empty their bladders in approximately 21 seconds.
Why specifically 21? According to the researchers, gravity is what enables urine to flow faster as the urethra lengthens. Large animals, like elephants, may store more urine, but they also have much longer urethras, so gravity plays a stronger role, and the flow is faster. In this case, the urethra functions like a “Pascal barrel” – a physics term that describes a situation in which a closed tube carrying liquid downward increases gravitational pressure on the liquid and speeds up its flow.
In contrast, very small animals like rats urinate in a fraction of a second – simply because the surface tension of their urine limits their flow rate. This is a physical property that causes liquids to cling to themselves, making it harder for them to pour out quickly when pressure is low.
This law, it turns out, is not only amusing – but also medically useful. The researchers developed an equation that makes it possible to calculate the expected urination time for any animal (including humans), and consistent deviation from this time may hint at bladder or urinary tract problems. The study has even proven especially useful in urology research using models of mice and pigs.
And what if it takes too long – or too little?
The 21-second rule isn’t meant to make you time every bathroom visit, but to serve as a general guideline. If you’re consistently urinating for much longer – you may be holding your urine for too long and overstretching your bladder, a condition that could impair its function in the long run. In rare cases, if there’s a blockage, it could also lead to a bladder rupture – a life-threatening condition.
On the other hand, if you urinate many times a day and only a small amount each time, you may be suffering from what’s called an overactive bladder – a feeling of urgency even when there isn’t much urine inside. It could also indicate bladder stones, cystitis (inflammation of the bladder), or prostate problems (in men).
“Changes in the duration of urination, especially if accompanied by pain, pressure, or discomfort, may indicate infections, stones, or prostate issues,” explained urologist Nicole Eisenbrown to the website Well and Good. She recommends measuring urination time as an average over a period, and not relying on a one-time experience.
Additionally, holding urine for long periods (a common occurrence in professions like teaching or nursing) may lead to urinary tract infections, since urine doesn’t empty completely, and bacteria multiply in that environment. It’s advisable to urinate when needed and not wait, and also to pay attention if the amount of time you spend in the bathroom has consistently changed.
Either way, the next time you go to the bathroom, pay attention to the time. If you consistently deviate from this average, it might be your body’s way of signaling that it’s worth getting checked.