Bladder Volume Calculator (ultrasound length × width × height × coefficient)

Understanding the bladder volume calculator — concept and principle

This calculator estimates bladder volume from three ultrasound measurements, length, width and height, multiplied by a correction coefficient. It also shows the raw box volume and the volume with the exact ellipsoid factor π/6. Nurses, sonographers and students use it, for example to estimate post-void residual urine.

Box × shape factor — with the default inputs: 262 mL.

How it is calculated

Volume (mL) = length × width × height (cm) × coefficient
Default coefficient 0.52, the ellipsoid factor π/6 rounded
Box volume = length × width × height
1 cm³ = 1 mL

Length and height are measured on a longitudinal (sagittal) view, width on a transverse view.

The principle

An ellipsoid with axes L, W and H has a volume of π/6 × L × W × H, about 52% of the box that encloses it. Treating the bladder as an ellipsoid gives a quick estimate from three measurements. Real bladders are flatter or more box-like depending on how full they are, so published coefficients range from about 0.5 to 0.8, and the error of a single estimate is often 10–25%. Measured straight after voiding, the result is the post-void residual (PVR).

Worked example

Defaults: length 9 cm, width 8 cm, height 7 cm, coefficient 0.52.

Box volume = 9 × 8 × 7 = 504 mL.
Estimated volume = 504 × 0.52 = 262 mL.
With π/6 = 0.5236: 264 mL.

Each point is the calculator re-run with only “Length – longitudinal view (cm)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Length – longitudinal view (cm)	Estimated bladder volume (mL)
2.25	66
4.5	131
6.75	197
9	262
11.2	328
13.5	393
18	524

How to read the result

There is no single agreed cut-off for post-void residual. A PVR under about 50 mL is generally regarded as normal, while larger or rising volumes are judged by a clinician together with symptoms. Use the coefficient your device or unit recommends, and repeat measurements if the result will change management.

Common mistakes

Measuring width on the same view as length.
Including the bladder wall in the measurements.
Mixing coefficients between visits.
Measuring long after voiding when assessing residual volume.

Keep in mind: Not a diagnosis. Bladder scanning and its interpretation should be done by trained staff.

Frequently asked questions

How is bladder volume calculated on ultrasound?

Length × width × height × a coefficient, commonly 0.52.

What is a normal post-void residual?

Generally under about 50 mL, but there is no single agreed cut-off.

Why is the coefficient 0.52?

It is π/6, the ratio of an ellipsoid's volume to its enclosing box.

Sources: Ellipsoid volume formula V = π/6 × L × W × H (standard geometry); bladder correction coefficients of about 0.5–0.8 reported in the ultrasound literature

Checked 9 Nov 2026. Ellipsoid volume formula V = π/6 × L × W × H (standard geometry); bladder-specific correction coefficients of about 0.5–0.8 reported in the ultrasound literature (standard value 0.52).

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