How Big are 6, 7 and 8 mm Kidney Stones

6mm, 7mm and 8mm kidney stones are .23 inches, .27 inches and .31 inches in width respectively, making an 8mm kidney stone about the size of a small kernel of corn.

A kidney stone is likely considered too large to pass on its own if it is larger than 5-8 mm in size. Kidney stones or nephrolithiasis may be able to pass unassisted through the ureter, bladder and urethra if they are less than 4-5 mm in size.

Definition: What is a kidney stone?

Kidney stones (nephrolithiasis) are the accumulation of different substances (such as different types of chemicals, acids, or minerals) in the kidney into a stone-like structure. These stones are released from the kidney into the ureter (the tube that carries urine from the kidneys into the bladder). Discomfort, symptoms and pain are experienced when these stones move their way through the ureter.

There are four different types of kidney stones named for or based on the substance from which they were formed.

What are the types of kidney stones?

The four types of kidney stones are:


Calcium oxalate stones are the most common type of kidney stone, caused by a build-up of calcium and oxalate or phosphate.

Uric Acid-

This type of kidney stone can be caused by urine that is too acidic; is a buildup of uric acid or uric acid and calcium. It may be helpful to try drinking some alkaline fluids.


Struvite kidney stones can be caused by urine that is too alkaline (can become too alkaline if one has certain types of urinary tract infections by a certain bacteria); stones are comprised of magnesium, phosphate and ammonium.


Cystine stones are rare and usually only found in people with genetic predisposition for a normal body chemical, called cystine, to abnormally leak from the kidney into urine.

Characteristics & Size of Kidney Stones & Ureters

Kidney stones can range in size from a grain of sand to several inches. The size and location will help determine how to best treat the stone, if it can pass on its own or not, and possible how to prevent them in the future.

Kidney stones are usually hard with jagged edges. Some are more jagged and some are smoother.

The ureter, part of the urinary tract system, is a tube (about 25-30 cm long) made of smooth muscle fibers. This tube that carries urine from the kidney to the bladder is on average 3-4 mm in diameter.

As it is a muscle that has some ability to expand and contract, kidney stones that are 5 mm (¼ inch) or less in size can move their way through the ureter on their own.

A kidney stone that is 6-7 mm or larger in size is likely too large to pass through the ureter and will need to be removed in another way.

The type of kidney stone and the size of the kidney stone can offer different treatment and management options.

Signs & Symptoms of kidney stones

  • How do you know if you have kidney stones?
  • What are the first signs of kidney stones?

Signs and symptoms of kidney stones may include:

  • Pain in the lower back or sides
  • Fever
  • Blood in urine
  • Decrease in urinary output (not peeing as much)

Kidneys, Ureters, BladderDiagnosis of kidney stones

If you think you might have a kidney stone, talk to your doctor. Your healthcare provider may do the following diagnostic tests:

  • Urine test
  • Blood test
  • Imaging test
  • Analysis of the passed stone

Prevention of kidney stones

  • How to prevent kidney stone?

Knowing what kind of kidney stone you are more prone to may help in the prevention. In general the number 1 way to avoid kidney stones is to stay hydrated.

The following list of tips may be helpful to prevent kidney stones:

  • Drink plenty of water throughout the day (64-96 ounces recommended).
  • Add lemon to the water you are drinking.
  • Eat less sodium and salt; eat less meat.
  • If you are more likely to develop a calcium-oxalate kidney stone, avoid foods high in oxalate.
  • Consider having your thyroid and parathyroid gland tested.
  • If you are more likely to develop a uric acid kidney stone, avoid foods high in uric acid.
  • If you are more likely to develop a struvite kidney stone, consider talking with your doctor about using a medication to prevent urinary tract infections and bacterial presence.

Frequently Asked Questions and Responses

  • How to get rid of kidney stone?
  • What can you drink to dissolve the stone?
  • How long does it take to pass the stone?

How to get rid of a kidney stone:

For stones that are expected to pass unassisted (less than 4-5 mm in size) the following home treatment options are recommended:

Drink Water!

Unless you have a medical condition where your physician does not recommend you to increase your water intake, drink 64-96 ounces of water daily. You should have clear or nearly clear colored urine. Drinking water may act as a flush to move the stone through the ureter more quickly and less painfully.

Pain Management:

Unless you have a medical condition that does not allow you to take over the counter pain medications such as Tylenol, Ibuprofen, or Aleve–take these medications according to package instructions. Pain can be mild to severe when passing a stone and pain is important to manage during this time.


Your physician, nephrologist or urologist may prescribe a medication that works as a muscle relaxant for you to help pass the stone. As mentioned previously, the ureter is a muscle, and taking a medication that allows it to relax and expand will aid in the passing of a kidney stone.

For stones that are not expected to be able to pass on their own (6-7 mm or larger) the following treatment options may be recommended:

Sound Waves:

This procedure is called an Extracorporeal Shock Wave Lithotripsy or ESWL, and essentially the idea is that sound waves (via ultrasound) are used to locate the kidney stone (from the outside of the body). Then sound waves are sent to the kidney stone which breaks it into smaller pieces that can pass through the ureter on their own. Sometimes, in very large stones, this needs to be done more than once in order to break up the smaller pieces even more. This treatment can be very effective and is successful in treating kidney stones that are up to 20 mm in size.


A Percutaneous Nephrolithotomy (PCNL) surgery may be a better option when other options are not available or were unsuccessful. In this surgical procedure, the kidney stone is accessed through an incision in the patient’s back and either removed or broken into smaller pieces that can pass on their own. This type of procedure is relatively successful in treating kidney stones that are 21-30 mm in size.


A ureteroscopy or Retrograde Intrarenal Surgery (RIRS) is when a scope is inserted (while the patient is under general anesthesia) into the urethra, through the bladder and into the ureter until the stone is located. Once located it may either be removed by the surgeon using a special tool, or broken into smaller pieces that can pass on their own. In this surgery a stent may be temporarily placed, allowing the pieces to drain into the bladder).

Parathyroid Gland Examination:

In people who have chronic or recurrent issues with calcium-oxalate kidney stones, the parathyroid gland (located near the throat) may be examined to see if it is over producing–which can cause calcium kidney stones to develop. If there is evidence of an overactive parathyroid hormone, (hyperthyroidism) surgery can be done or medication prescribed to correct the overactive gland.

Dissolving the stone:

Dietary changes may help to break up, dissolve or shrink the kidney stone–especially if you have a Calcium or Uric Acid stone, as these substances may be acquired through diet.

Calcium Kidney Stone

Calcium-based foods do not cause kidney stones, but calcium supplements can. Make sure you check with your doctor to see if you should stop taking a calcium supplement or continue (make sure you are taking it with food).

In calcium stones, the oxalate that combines with the calcium to form the stone can be acquired through diet and these foods should be avoided: spinach, swiss chard, okra, bran flakes, rhubarb, soy products, french fries, potato chips, sweet potatoes, chocolate, tea, black pepper and nuts.

Uric Acid Kidney Stone

Avoid acidic juices and foods that may cause your urine to be more acidic. Also avoid foods that contain high amounts of uric acid such as: alcohol, organ meats (liver, kidney), spinach, sardines and some other fish and seafood, bacon, turkey, veal and venison.

Surprisingly, lemons have been known to help prevent the formation of kidney stones. Try adding a few slices of lemon or splashes of lemon juice to your water.

I have a kidney stone–so what does that mean?

If you think you have a kidney stone, call your doctor. Likely they will want to see you in the office. They may do an imaging test to determine the size and location of the stone in order to determine what treatment options are best. If it is small enough to pass on its own you will be expected to return home and wait for the stone to pass.

So you or someone you know has a kidney stone. If it is less than 5 mm in size and expected to pass on its own, patience. It can take several days to pass a kidney stone, and can be very painful. Make sure you are drinking lots of water, using over the counter pain medication, perhaps a warm bath or heating pad may be helpful in providing pain relief.

Use a strainer when you pee. (Not one from the kitchen!) Your doctor may be able to provide you with a urinary strainer if they want you to collect the kidney stone for analysis. If not, a stocking or cloth maybe used. You doctor will likely want to see the stone for further examination. This will also confirm if you have passed the stone or not.

Take your temperature if you suspect that you have a fever.

If you have fever, sudden increase of severe pain, or episode of shaking or shivering call your doctor immediately.

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