Passing a kidney stone is a process that unfolds over hours to weeks, and it changes what you see in the toilet, what you feel in your body, and what your urine looks like at each stage. Most small stones (under 5 mm) pass on their own, but even tiny ones can cause significant pain and visible changes in your urine along the way.
What the Stone Itself Looks Like
When a kidney stone finally comes out, it can be surprisingly small for the amount of pain it caused. Many stones are just a few millimeters across, roughly the size of a grain of sand or a small pebble. Their shapes vary widely: some are smooth and round, others are jagged, barbed, or angular with rough edges. The spiky ones tend to cause more discomfort as they scrape along the lining of your urinary tract.
Color depends on what the stone is made of. The most common type, calcium oxalate, tends to be dark brown or black with a rough, uneven surface. Calcium phosphate stones are usually smoother and pale yellow to tan. Uric acid stones range from yellowish to reddish-brown. Some stones are whitish or caramel-colored, and others are mottled with multiple shades. When you catch one in a strainer, it often looks like a small, oddly shaped grain of gravel.
What Your Urine Looks Like During Passage
One of the first visual signs that a stone is moving is a change in your urine. As the stone scrapes the lining of your ureter (the narrow tube connecting your kidney to your bladder), it causes bleeding. This can make your urine look pink, red, or brown. Sometimes the color change is dramatic, other times it’s faint enough that you might describe it as tea-colored or slightly off.
Your urine may also appear cloudy or have a stronger, more unpleasant smell than usual. If blood clots form, you might notice small dark strings or clumps in the toilet. Passing those clots can be painful on their own, and they can briefly block urine flow, making it feel like you’re straining to go. Not everyone sees visible blood. In some cases the bleeding is microscopic and only shows up on a urine test.
How the Pain Moves as the Stone Moves
The pain pattern tells you roughly where the stone is in your system. It typically starts as a deep, intense ache in your flank, the area between your lower ribs and hip on one side. This is called renal colic, and it happens when the stone drops out of the kidney and enters the ureter.
As the stone travels down the ureter, the pain often shifts. It can radiate to your back, wrap around toward your lower abdomen, or shoot down into your groin. Many people describe it as coming in waves: several minutes of excruciating cramping followed by a brief lull, then another wave. The waves correspond to your ureter squeezing and spasming as it tries to push the stone along. You may also feel nausea, and vomiting is common during the worst episodes.
Once the stone drops into your bladder, the intense flank pain usually stops relatively abruptly. From there, it typically passes within a few days. The final stretch, moving from the bladder out through the urethra, is usually much less painful than the journey through the ureter, though you may feel pressure, burning, or a brief sharp sting as it exits.
How Long the Whole Process Takes
The timeline depends almost entirely on the stone’s size. Stones smaller than 4 mm pass on their own about 76% of the time, often within a few days to two weeks. Stones between 5 and 7 mm still pass without intervention roughly 60% of the time, but the process can take several weeks. Once stones reach 8 mm or larger, the odds of passing naturally drop to around 50% or less, and stones over 9 mm pass on their own only about 25 to 33% of the time.
During this waiting period, you may have stretches where you feel completely fine, only to have another round of pain when the stone shifts position. This start-and-stop pattern is normal and doesn’t mean something has gone wrong.
What to Watch for in the Toilet
Your doctor will likely ask you to strain your urine so the stone can be analyzed. The simplest method is urinating through a fine kitchen strainer or a tea strainer every time you go. After each use, check the strainer for any small, hard particles. When you find the stone, store it in a small plastic bag or container and bring it to your next appointment. Lab analysis reveals what the stone is made of, which helps guide dietary changes to prevent the next one.
Some people feel the stone pass and know the exact moment. Others find it in the strainer without having noticed anything unusual. Either experience is normal.
Medications That Help Stones Pass
For stones between 5 and 10 mm, doctors sometimes prescribe a medication that relaxes the muscles in your ureter, making it easier for the stone to slide through. This approach significantly improves expulsion rates for larger stones, shortens the time to passage, and reduces the number of painful colic episodes along the way. For stones 5 mm and smaller, the medication doesn’t appear to make a meaningful difference since those stones already have a high chance of passing on their own.
Signs That Need Immediate Attention
Most kidney stones pass with time, fluids, and pain management. But certain symptoms signal that the stone is causing a complication. A fever or chills alongside stone pain can indicate an infection trapped behind the blockage, which can escalate quickly. Complete inability to urinate means the stone may be fully obstructing your urinary tract. Persistent vomiting that keeps you from staying hydrated is another reason to get help fast. If the pain becomes truly unmanageable despite over-the-counter relief, or if you notice heavy, sustained blood in your urine, those also warrant urgent evaluation. An untreated obstruction can lead to kidney infection or threaten long-term kidney function.
The standard imaging used to locate a stone and determine its size is a CT scan without contrast dye. It shows exactly where the stone is sitting, how large it is, and how dense it is, which helps your doctor decide whether you can wait it out or need a procedure to remove it.