Passing a kidney stone is one of the most painful experiences in medicine. Patients rate the pain at roughly 7.9 out of 10 on average, and nearly 89% of men and 78% of women describe it as the worst pain they’ve ever felt. Among women who have been through both kidney stones and childbirth, 63% say the stone was worse.
Why Kidney Stones Hurt So Much
The pain doesn’t come from the stone cutting tissue, as many people assume. It comes from pressure. When a stone drops out of the kidney and enters the ureter (the narrow tube connecting your kidney to your bladder), it can block the flow of urine. Urine backs up, the kidney swells, and the fibrous capsule surrounding the kidney stretches. That stretching activates pain and stretch receptors throughout the kidney, renal pelvis, and ureter simultaneously.
On top of that, the ureter goes into spasm, contracting repeatedly to try to push the stone along. The tissue around the blockage becomes inflamed, which amplifies the pain signal further. This combination of organ swelling, muscle spasm, and inflammation is why kidney stone pain (called renal colic) hits so hard and comes in waves rather than staying constant.
The intense nerve activation also triggers your autonomic nervous system, which is why many people experience nausea, vomiting, and cold sweats during an episode. These aren’t separate problems. They’re your body’s reflexive response to the severity of the pain signal.
How the Pain Changes as the Stone Moves
The location of pain shifts as the stone travels. It typically starts as a deep ache high in the back, near the kidney on the affected side. As the stone moves down the ureter, the pain migrates toward the front of the abdomen. Once it reaches the lower ureter near the bladder, you’ll often feel it in the groin or inner thigh. Near the end, when the stone is close to entering the bladder, many people feel a strong, persistent urge to urinate.
The pain is not constant throughout. It tends to come in intense waves lasting 20 to 60 minutes, separated by periods of relative calm. These waves correspond to the ureter contracting against the stone and urine pressure building behind it. Once the stone drops into the bladder, the worst pain is usually over. Passing it from the bladder through the urethra is generally much less painful, though you may feel some burning or pressure.
Stone Size Determines Everything
The size of a kidney stone is the single biggest factor in how painful the experience will be, how long it lasts, and whether you’ll pass it without a procedure. Research tracking hundreds of stones over 20 weeks found clear thresholds.
- Under 3 mm: About 98% pass on their own. These are the quickest to resolve, averaging around 31 days, though many pass much sooner.
- 4 mm: Around 81% pass spontaneously, typically within about 31 days as well.
- 5 mm: The success rate drops to about 65%, and the average timeline stretches to around 45 days.
- 6 mm: Only about 33% pass on their own.
- 6.5 mm and larger: Just 9% pass without intervention. Stones this size almost always require a procedure.
Location matters too. Stones that have already traveled close to the bladder pass without intervention about 79% of the time, while stones still near the kidney pass on their own only 48% of the time. A stone closer to the bladder means less distance to travel and, usually, less total time in pain.
How It Compares to Childbirth
The kidney stone versus childbirth comparison comes up constantly, and there’s actual data on it. A study published in the Journal of Pain Research surveyed women who had experienced both. Of those 19 women, 63.3% said kidney stone pain was worse than childbirth, 15.7% said the two were about equal, and only 21% said childbirth hurt more.
Interestingly, men tend to underestimate their own pain relative to childbirth. In the same study, 40% of male kidney stone patients guessed that childbirth was probably worse, and another 23.4% figured the two were comparable. On the Visual Analog Scale, kidney stone pain averages a score of 73.3 out of 100, which places it in the same range as active labor.
What Pain Relief Looks Like
For most people passing a stone at home, over-the-counter anti-inflammatory painkillers are the first line of defense. These work by reducing the inflammation around the stone, which directly addresses one of the main pain drivers. Stronger prescription pain relief is sometimes needed for breakthrough episodes.
You may have heard of medications that relax the ureter to help stones pass faster. A large randomized trial tested this approach in emergency department patients with stones under 9 mm and found no significant benefit. The passage rate with the medication was 49.6%, compared to 47.3% with a placebo, and time to passage was essentially the same. Your doctor may still prescribe it in certain situations, but the evidence for a clear advantage is limited.
Drinking plenty of water helps by increasing urine flow, which pushes the stone along and reduces the concentration of urine behind the blockage. Staying active, when the pain allows it, may also help with movement of the stone.
Signs That Need Immediate Attention
Most kidney stones, especially small ones, pass safely at home with pain management. But certain symptoms during a stone episode signal something more dangerous is happening. A fever above 37.5°C (99.5°F) alongside stone pain suggests infection behind the blockage, which can escalate quickly into sepsis. Other red flags include pain that doesn’t respond to any medication, complete inability to keep fluids down due to vomiting, or producing little to no urine. If you have only one functioning kidney and suspect a stone, the urgency is higher because a single blockage can compromise all of your kidney function at once.