Educational tool — not a diagnosis. This applies a published formula to numbers you enter. Organ volume is interpreted by clinicians alongside body size, symptoms, blood results and other imaging findings.
Discuss any result with the healthcare professional who arranged your scan. A single volume neither confirms nor excludes any condition.
Quick answer: volume = length × width × height × 0.524, with diameters in centimetres. An 11 × 7 × 4 cm spleen is about 161 mL. Splenomegaly is often described above roughly 300–500 mL, but the threshold depends on body size and the reference used.
The formula
Both the spleen and the kidney are modelled as prolate ellipsoids using the standard π/6 coefficient. Worked example — a spleen measuring 12.5 × 7.0 × 4.5 cm:
- Multiply the diameters: 12.5 × 7.0 × 4.5 = 393.75
- Apply the coefficient: 393.75 × 0.524 = 206.3 mL
The ellipsoid (π/6) method is standard for organ volume estimation on ultrasound. For the spleen, craniocaudal length over about 12–13 cm is a common screening threshold; volume gives a fuller measure. Reference ranges vary with body size, sex and population.
Reference figures
| Organ | Commonly cited volume | Enlargement described above |
|---|---|---|
| Spleen (adult) | ≈ 100–300 mL | ≈ 300–500 mL (splenomegaly) |
| Kidney (each, adult) | ≈ 120–200 mL | Varies by cause and body size |
These are broad orientation figures, not fixed cut-offs. Splenic and renal volume scale with body size, so thresholds are often adjusted for height or body surface area, and interpretation always depends on why the scan was requested.
Splenic index — and why it is not the same as splenic volume
Radiology reports often quote a splenic index rather than a volume, and the two are related but distinct. The splenic index is simply the product of the three diameters, with no geometric coefficient applied:
Splenic volume (ellipsoid) = L × W × T × 0.524
Splenic volume (Koga regression) = 30 + 0.58 × splenic index
Taking the same 12.5 × 7.0 × 4.5 cm spleen from the worked example above:
| Quantity | Calculation | Result |
|---|---|---|
| Splenic index | 12.5 × 7.0 × 4.5 | 393.8 cm³ |
| Volume, ellipsoid | 393.8 × 0.524 | 206.3 mL |
| Volume, Koga | 30 + 0.58 × 393.8 | 258.4 mL |
Those two volume figures differ by 52 mL — about 25%. That is not a rounding discrepancy; they are different models. The ellipsoid formula assumes the spleen is a smooth prolate ellipsoid, which systematically under-reads because a real spleen is more irregular. The Koga regression was fitted to measured splenic volumes and includes a constant offset, which is why it runs higher. Neither is wrong — but a volume quoted without saying which method produced it is ambiguous, and you cannot meaningfully compare a Koga volume on one scan with an ellipsoid volume on the next.
| Splenic index | Commonly described as |
|---|---|
| < 120 cm³ | Small |
| 120 – 480 cm³ | Within the usual adult range |
| > 480 cm³ | Enlarged — splenomegaly |
| > 1,000 cm³ | Marked splenomegaly |
The 480 cm³ splenic index threshold and the Koga regression are widely cited in the radiology literature. Like all such figures they are population-derived orientation values, not diagnostic criteria, and splenic size scales with body habitus. Record which method you used, and keep to the same one when following a spleen over time.
Frequently asked questions
How is spleen volume calculated?
With the ellipsoid formula: volume = length × width × height × 0.524, using three perpendicular diameters in centimetres. A spleen measuring 11 × 7 × 4 cm gives 308 × 0.524 ≈ 161 cm³. Because 1 cm³ equals 1 mL, the result is in millilitres.
What is a normal spleen volume?
Adult splenic volume is commonly cited as roughly 100 to 300 mL, though it varies with body size, sex and the reference source. Volume above about 300 to 500 mL is often described as splenomegaly, but the threshold depends on the patient and the guideline used.
How is splenomegaly assessed on ultrasound?
Often by the spleen's craniocaudal length rather than volume — a length over about 12 to 13 cm is a common screening threshold. Volume gives a fuller picture but needs three measurements. Both are interpreted alongside the clinical context, since a normal-sized spleen does not exclude disease and a large one is not always pathological.
Can I use this for kidney volume?
Yes. The same ellipsoid formula is used for renal volume with the same coefficient, and it is applied to each kidney separately. Adult kidney volume is commonly around 120 to 200 mL per kidney, and the method is used in kidney donor assessment and in monitoring conditions such as polycystic kidney disease.
How accurate is the ellipsoid method for these organs?
It is a good approximation for a regularly shaped organ but is only an estimate. The spleen in particular can be irregular, and because three measurements are multiplied, errors compound. Cross-sectional imaging with 3-D reconstruction is more accurate when precision matters.
References
- Prolate ellipsoid volume formula — standard geometric derivation, V = (π/6) × d₁ × d₂ × d₃.
- General references on splenic length and volume thresholds for splenomegaly on ultrasound.
- References on renal volume estimation by the ellipsoid method in donor assessment and polycystic kidney disease.