A passed kidney stone typically looks like a small grain of sand or a tiny piece of gravel sitting in your strainer or toilet bowl. Most are brown, tan, or yellowish, though the exact color and texture depend on what the stone is made of. They range from smaller than a pinhead to the size of a pencil eraser, and the experience of passing one changes noticeably as the stone moves through your urinary tract.
What the Stone Itself Looks Like
Kidney stones vary in color, shape, and surface texture based on their chemical makeup. The most common type, calcium oxalate, tends to be brown to dark brown with a bumpy, rough surface. Some have a lumpy, budding texture, while others are smoother with a pale beige or cream color. These are the stones most people picture when they think of kidney stones.
Uric acid stones look quite different. They’re typically orange, sometimes shifting toward cream or ochre, and their surface can be smooth and uniform or rough and porous with an uneven color that blends beige and brown-orange. Struvite stones, which form in the setting of urinary infections, are whitish with blunted edges and a more uniform appearance. Regardless of type, most stones that pass on their own are small enough to sit on your fingertip.
What Your Urine Looks Like During Passage
One of the first visual signs that a stone is moving is a change in your urine. Blood in the urine is common, ranging from a faint pink tinge to visibly red or brown. This happens because the stone scrapes the lining of the ureter and urethra as it travels. Your urine may also look cloudy or have a stronger smell than usual, especially if there’s an accompanying infection. Near the very end, as the stone exits, you may notice your urine turning brown or see small particles in the toilet.
How Pain Shifts as the Stone Moves
The passage happens in distinct stages, and the pain changes location and character at each one. Understanding this progression helps you make sense of what your body is doing.
While the stone is still in the kidney, you may feel sharp, intermittent pain in your back or side that resembles a muscle strain. The kidney contracts to push the stone out, creating waves of pain that come and go. Once the stone drops into the ureter (the narrow tube connecting your kidney to your bladder), the pain shifts. It becomes more of a constant, throbbing ache as the stone scrapes along the urinary tract walls. Many people feel this pain radiate from the flank down toward the lower abdomen and groin.
When the stone reaches the bladder, most of the sharp pain disappears. What replaces it is intense pressure and a relentless urge to urinate, sometimes as often as every five minutes. Your body is working to push the stone the final stretch. The last stage involves passing the stone through the urethra and into the toilet. This can involve a final burst of sharp pain, and you may need to push. If you’re straining your urine (which you should be), this is the moment you’ll actually see the stone caught in the mesh.
How Long the Whole Process Takes
The timeline varies widely depending on stone size and location. Stones 2 mm or smaller take an average of about 8 days to pass, though for 95% of people it can take up to 31 days. Stones between 2 and 4 mm average around 12 days, with some taking up to 40 days. Stones 4 mm and larger average about 22 days, and roughly half of stones over 5 mm will eventually need medical intervention because they simply won’t pass on their own.
Stones closer to the bladder and on the right side tend to pass faster. Pain level, age, and gender don’t predict how long it will take.
Which Stones Pass and Which Won’t
Size is the single biggest factor in whether a stone will pass without help. Stones under 3.5 mm pass on their own about 98% of the time. At 3.5 to 4.4 mm, that drops to around 81%. Between 4.5 and 5.4 mm, about 65% pass spontaneously. Once a stone reaches 5.5 to 6.4 mm, only about one in three will make it through. Stones 6.5 mm and larger have roughly a 9% chance of passing without intervention.
Current urology guidelines allow for a trial of passage with medication for stones up to 10 mm in the lower ureter, giving it approximately 30 days before considering a procedure. The medication relaxes the muscles of the ureter to help the stone slide through more easily.
How to Catch and Keep the Stone
Your doctor will likely ask you to strain every single urination through a fine mesh strainer (usually provided at the hospital or pharmacy). Check the strainer carefully each time. The stone may be tiny enough to mistake for a grain of sand or a speck of sediment, so look closely.
When you find it, place it in a clean, dry container with a lid. Don’t wrap it in tissue, tape it to anything, or add fluid. The lab needs the stone dry and uncontaminated to analyze its composition. That analysis determines what type of stone you formed, which directly shapes the dietary and medical plan to prevent future ones.
Signs That Need Immediate Attention
Most kidney stones, while painful, pass safely at home. But certain symptoms signal a situation that can turn dangerous quickly. Fever alongside kidney stone pain suggests infection, which can progress to sepsis if the infected urine is trapped behind the stone. Vomiting so severe that you can’t keep fluids down puts you at risk of dehydration and means oral pain medication won’t work. Complete inability to urinate, or pain that becomes truly unmanageable, also warrants emergency evaluation. People with a single kidney, a kidney transplant, or stones blocking both sides face higher risk and need faster intervention.