What size stones are generally expected to pass on their own?

Stones that are typically expected to pass spontaneously through the urinary tract are generally around 5 mm or smaller in size. The likelihood of passage decreases as the size of the stone increases.

Stones that are about 5 mm in diameter have an adequate chance of passing without intervention, as they can navigate through the ureter and bladder with relative ease. Clinical studies indicate that stones larger than this, particularly those around 6 mm or greater, show a significantly reduced passage rate and may often require medical or surgical intervention for removal.

Smaller stones, such as those measuring 2 mm, 3 mm, and 4 mm, are also known to pass on their own, but the threshold for optimal spontaneous passage is generally considered to be around 5 mm. Therefore, while smaller stones are likely to pass, the definitive size at which many clinicians expect a stone to pass on its own is 5 mm, making this answer particularly representative of standard urological practice.