How Hard Is a Kidney Stone?

Kidney stones are hard pebble-like objects that can form inside your kidneys. They're made of minerals and salts. You might hear your doctor call them renal calculi, nephrolithiasis, or urolithiasis. Kidney stones are small -- usually between the size of a kernel of corn and a grain of salt.

Is a kidney stone hard or soft?

A kidney stone is a buildup of solid material that clumps together within the urine and forms within the kidney. Kidney stones are usually hard because they are made up mainly of crystals. Almost all (98%) of the kidney stone weight is made up of crystals. But kidney stones also have soft mushy parts called matrix.

How hard is it to pass a kidney stone?

Size of the stone is a major factor in whether it can pass naturally. Stones smaller than 4 millimeters (mm) pass on their own 80 percent of the time. They take an average of 31 days to pass. Stones that are 4–6 mm are more likely to require some sort of treatment, but around 60 percent pass naturally.