Quick answer: kidney volume = length × width × depth × 0.523, with all three diameters in centimetres and the answer in millilitres. A kidney measuring 11 × 5.5 × 4.5 cm holds about 142 mL. Normal adult kidneys run roughly 110–170 mL each. For polycystic kidney disease, add both kidneys and divide by height in metres to get htTKV.
Educational tool, not medical advice. Kidney volume is interpreted alongside kidney function, imaging appearance, symptoms and history. A number outside a published range does not by itself indicate disease. Do not use this page to interpret your own scan results — discuss them with the clinician who ordered them.
The ellipsoid formula
L = craniocaudal length · W = width · D = anteroposterior depth · all in cm, V in mL
A kidney is modelled as a prolate ellipsoid — a rugby-ball shape — and 0.523 is π/6, the fraction of the enclosing box that an ellipsoid actually fills. It is the same coefficient used for prostate, ovarian and thyroid volume, because all four organs are approximately ellipsoidal.
Worked example — a right kidney measuring 11.0 cm long, 5.5 cm wide, 4.5 cm deep:
- Multiply the diameters: 11.0 × 5.5 × 4.5 = 272.25 cm³
- Apply the coefficient: 272.25 × 0.523 = 142.4 mL
Getting the measurements right matters more than the arithmetic. The three diameters must be mutually perpendicular. Length is taken as the maximum craniocaudal dimension in the coronal plane — and where both coronal and sagittal lengths are available, the convention is to average them, because a single plane rarely catches the true long axis. Width and depth are then measured on a transverse image, perpendicular to that length axis and to each other. An off-axis length measurement is the single largest source of error, and because all three terms multiply, a 5% error in each compounds to roughly 15% in the volume.
Reference ranges
| Measure | Adult men | Adult women | Notes |
|---|---|---|---|
| Length | 10–12 cm | 9–11.5 cm | The figure most often reported on ultrasound |
| Width | 5–7 cm | 4.5–6.5 cm | |
| Depth (AP) | 4–5 cm | 3.5–4.5 cm | Hardest to measure reproducibly |
| Volume, single kidney | ~145 mL | ~125 mL | Typical means; usual range ~110–170 mL |
| Total kidney volume | ~290 mL | ~250 mL | Both kidneys combined |
| Left vs right | Left usually slightly larger | The liver limits the right kidney | |
Reported means vary between published series depending on imaging modality and population. Kidney volume scales with body size, so these figures are context for a measurement rather than diagnostic thresholds.
Kidney volume falls with age from roughly the fifth decade onwards, and it falls faster than length does — which is part of why volume is a more sensitive measure of parenchymal loss than the length figure that gets reported routinely.
Total kidney volume and why it matters in ADPKD
In autosomal dominant polycystic kidney disease, cysts accumulate over decades and the kidneys enlarge — sometimes to many litres. The important clinical fact is about timing: total kidney volume starts rising long before eGFR starts falling.
The kidney compensates by hyperfiltration through the remaining healthy tissue, so blood tests can look reassuring for years while the structural disease advances steadily. By the time creatinine moves, a great deal of parenchyma has already been lost. TKV picks the process up much earlier, which is why it became the accepted progression marker and why it is used as an endpoint in ADPKD trials.
htTKV = TKV ÷ height in metres (mL/m)
Why divide by height. Larger people have larger kidneys. Without adjustment, a 1.9 m patient looks worse than a 1.55 m patient with identical disease. Dividing by height in metres removes most of that body-size effect and is what makes the figure comparable between patients.
| Mayo class | Estimated htTKV growth | Broad implication |
|---|---|---|
| 1A | < 1.5% per year | Slowest progression |
| 1B | 1.5 – 3% per year | Slow |
| 1C | 3 – 4.5% per year | Intermediate |
| 1D | 4.5 – 6% per year | Rapid |
| 1E | ≥ 6% per year | Most rapid progression |
| Class 2 | n/a — atypical morphology | Asymmetric or atypical imaging; the class 1 model does not apply |
Class is assigned from htTKV and age together, using the Mayo model's published curves — not from htTKV alone. This calculator gives you htTKV; assigning a Mayo class requires the official classification tool and a clinician's confirmation that the imaging is typical (class 1) rather than atypical (class 2).
An important limitation, stated plainly. The ellipsoid formula systematically underestimates volume in polycystic kidneys. Three straight-line measurements cannot capture a lumpy, irregular cystic contour, and the error grows as the kidneys distort. Published comparisons put ellipsoid estimates several percent below segmentation-derived volumes in ADPKD, with the gap widening in advanced disease. For research, trial enrolment or a treatment decision, manual or semi-automated segmentation from MRI or CT is the reference standard. Use this calculator for orientation, not for classification.
Kidney volume by dimensions — quick reference
Volumes for common measurement combinations, so you can sanity-check a figure quickly.
| Length × Width | D = 3.5 cm | D = 4.0 cm | D = 4.5 cm | D = 5.0 cm |
|---|---|---|---|---|
| 9.0 × 4.5 cm | 74 mL | 85 mL | 95 mL | 106 mL |
| 10.0 × 5.0 cm | 92 mL | 105 mL | 118 mL | 131 mL |
| 10.5 × 5.0 cm | 96 mL | 110 mL | 124 mL | 137 mL |
| 11.0 × 5.5 cm | 111 mL | 127 mL | 142 mL | 158 mL |
| 11.5 × 5.5 cm | 116 mL | 132 mL | 149 mL | 165 mL |
| 12.0 × 6.0 cm | 132 mL | 151 mL | 169 mL | 188 mL |
| 12.5 × 6.0 cm | 137 mL | 157 mL | 177 mL | 196 mL |
| 13.0 × 6.5 cm | 155 mL | 177 mL | 199 mL | 221 mL |
Notice how quickly volume moves. Going from 10.0 × 5.0 × 4.0 to 12.0 × 6.0 × 5.0 — dimensions that both sound unremarkable on a report — nearly doubles the volume, from 105 to 188 mL. That sensitivity is exactly why volume detects change that a length measurement alone will miss, and equally why sloppy measurement produces misleading volumes.
Left versus right
A modest size difference between kidneys is normal — the left is usually a little larger, because the liver sits above the right kidney and constrains it. Differences up to roughly 10–15% are unremarkable.
Larger asymmetry has a short differential worth knowing:
- Compensatory hypertrophy — one kidney enlarges because the other is small, scarred or absent. The big kidney is the healthy one.
- Scarring from childhood reflux nephropathy, previous pyelonephritis, or infarction — the small kidney is the abnormal one.
- Renal artery stenosis — chronic underperfusion shrinks the affected side.
- Obstruction — an obstructed kidney is initially enlarged with a dilated collecting system, then shrinks if the obstruction persists.
- Measurement error — always worth excluding first, particularly if the difference appears on one scan and not the next.
The calculator flags the percentage difference between sides when you enter both.
Common mistakes & pro tips
- Measuring length off-axis. An oblique cut through a kidney under-reads its true long axis. This is the dominant error source, and averaging the coronal and sagittal lengths helps.
- Non-perpendicular diameters. The three measurements must be mutually at right angles; otherwise the ellipsoid model does not apply.
- Applying the ellipsoid formula to polycystic kidneys and treating it as definitive. It under-reads, progressively so in advanced disease.
- Comparing ultrasound to MRI volumes over time. Modalities differ systematically. Track with one.
- Forgetting to divide htTKV by height in metres. Using centimetres gives a figure 100× too small.
- Reading a single volume as normal or abnormal in isolation. Kidney size scales with body size; a 105 mL kidney is normal in a small adult and small in a large one.
- Pro tip — record the three diameters, not just the volume. It lets anyone recompute later, and makes measurement drift visible across serial scans.
- Pro tip — for serial monitoring, keep the operator constant if you can. Inter-observer variability on ultrasound renal volume is larger than most real year-on-year change.
How to use this calculator
- Choose one kidney or both. Both-kidney mode gives total kidney volume and the asymmetry check.
- Enter the three diameters in centimetres. Length, width and anteroposterior depth, mutually perpendicular.
- Add patient height in both-kidney mode to get height-adjusted TKV in mL/m.
- Optionally change the coefficient — 0.523 is standard; 0.49 is used in some paediatric and research protocols.
Frequently asked questions
How do you calculate kidney volume?
Multiply three orthogonal diameters and a coefficient: volume = length × width × depth × 0.523. The coefficient is π/6, which is the volume factor for a prolate ellipsoid. A kidney measuring 11 × 5.5 × 4.5 cm has a volume of about 142 mL. The same formula is used on ultrasound, CT and MRI.
What is a normal kidney volume?
Adult kidneys typically measure between about 110 and 170 mL each, with reported means around 145 mL in men and 125 mL in women. Kidney length is more commonly quoted than volume and is usually 10–12 cm. The left kidney is normally slightly larger than the right. Volume varies with body size, so a small adult with 100 mL kidneys may be entirely normal.
What is total kidney volume used for?
Total kidney volume is the sum of both kidneys and is the standard measure of disease burden in autosomal dominant polycystic kidney disease. It rises as cysts accumulate, and it does so long before estimated glomerular filtration rate starts to fall, which makes it a much earlier marker of progression than blood tests. It is also used to assess donor kidneys before transplant and to follow kidneys after transplantation.
What is height-adjusted total kidney volume?
Height-adjusted total kidney volume, or htTKV, is total kidney volume divided by the patient's height in metres, giving mL/m. Dividing by height removes the effect of body size, so a tall person with naturally larger kidneys is not misclassified as having more advanced disease. Together with age it forms the Mayo Clinic Imaging Classification, which sorts typical polycystic kidney disease into classes 1A through 1E by estimated growth rate.
How accurate is the ellipsoid formula for kidney volume?
It is good for kidneys of normal shape, usually within about 10% of volumes measured by planimetry or stereology. It becomes progressively less reliable as the kidney departs from a smooth ellipsoid, and in polycystic kidney disease it systematically underestimates volume because irregular cystic contours are not captured by three straight-line measurements. Where the number will drive a treatment decision, segmentation from MRI or CT is the reference method.
Why is one kidney bigger than the other?
A modest difference is normal, and the left kidney is usually slightly larger than the right, partly because the liver sits above the right kidney. Differences of up to about 10–15% are common. A larger asymmetry can be significant: one kidney may enlarge to compensate for a smaller or poorly functioning partner, or a kidney may be scarred and shrunken from previous reflux, obstruction or vascular disease. Persistent marked asymmetry is worth investigating.
References & further reading
- Irazabal, M. V. et al., Mayo Clinic Imaging Classification of ADPKD — htTKV and age-based risk classes.
- RadioGraphics, "Autosomal Dominant Polycystic Kidney Disease: Role of Imaging in Diagnosis and Management" — ellipsoid versus segmentation methods for TKV.
- CRISP (Consortium for Radiologic Imaging Studies of Polycystic Kidney Disease) — the studies establishing TKV as a progression marker.
- KDIGO controversies conference on ADPKD — role of imaging in risk stratification.
Educational use only. This calculator applies a published geometric formula. It does not assign a Mayo class, does not account for atypical imaging, and is not a diagnostic tool. See our accuracy policy.