How this calculator works
Measure three perpendicular bladder dimensions. The empirical coefficients come from Bih and colleagues; the geometric ellipsoid uses pi/6 and is a different model. A custom coefficient lets a laboratory use its own validated protocol. The optional reference comparison reports an observed difference, not a confidence interval. Measurement technique and irregular anatomy affect accuracy. The result is an estimate for information only and is not medical advice.
Formula
Volume = coefficient × dimension 1 × dimension 2 × dimension 3. With centimetres the volume is in cm³, numerically equal to mL. A missing dimension = known volume / (coefficient × the other two dimensions).
Worked example
Dimensions 8 × 6 × 5 cm with coefficient 0.72 give 172.8 mL. The empirical cuboid coefficient 0.89 gives 213.6 mL for the same measurements.
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Frequently asked questions
Why is the empirical ellipsoid coefficient not pi/6?
It is a fitted ultrasound coefficient for the shapes in the study. The geometric ellipsoid is offered separately.
What does the error output mean?
It is estimated volume minus your measured reference. The relative difference divides that error by the reference volume.
Does a post-void volume diagnose retention?
No. Timing, symptoms, measurement quality and the clinical context matter.