Gallbladder Stone Calculator
The Gallbladder Stone Calculator estimates stone volume and size classification based on ultrasound-measured diameter. This tool helps clinicians and patients monitor gallstone severity and assess obstruction risks. Whether tracking growth over time or evaluating symptoms, this calculator provides quick clinical estimates.
How Stone Volume Is Calculated
Stone volume is estimated using the geometric formula for a sphere. This assumes the gallstone is roughly round, which is a standard clinical approximation for monitoring purposes.
V = (4/3) × π × r³
Where:
- V = Volume of the stone (mm³)
- π = Pi (approximately 3.14159)
- r = Radius of the stone (Diameter ÷ 2)
- The diameter is divided by 2 to find the radius.
- The radius is cubed (multiplied by itself three times).
- The result is multiplied by Pi and 4/3.
- This gives the estimated volume in cubic millimeters (mm³).
While real gallstones are often irregular, this formula provides a consistent baseline for tracking changes in size over time.
What Your Stone Volume Means
The calculated volume and size category help determine the likelihood of complications and the urgency of medical intervention.
Clinical Scenarios
For Stones < 5mm: These are classified as "Very Small." While they may pass spontaneously, small stones carry a higher statistical association with migrating into the bile ducts and causing obstruction.
For Stones 5–20mm: These "Small" to "Medium" stones are the most common cause of biliary colic. They are generally too large to pass through the cystic duct safely but small enough to move within the gallbladder, blocking the duct.
For Stones > 20mm: "Large" stones are less likely to cause acute obstruction by moving into the duct, but they can irritate the gallbladder wall over time, increasing the statistical association with cancer or requiring surgical removal (cholecystectomy).
Calculation logic verified using publicly available standards.
View our Accuracy & Reliability Framework →