Thyroid volume
Calculate thyroid volume on ultrasound with the Brunn formula: length × width × depth × 0.479 per lobe, with the reference limits for goitre.
Right lobe
Left lobe
Total
12.2mL
Right
6.6mL
Left
5.6mL
Total 12.2 mL
The total volume of 12.2 mL falls within the commonly used upper limit of 18 mL for women.
The isthmus is not included in this formula. If it is clearly thickened, mention that separately rather than inflating the volume, or your measurement stops being comparable with earlier studies.
Upper limits differ between sources and populations, partly through iodine intake. Use them for orientation and, on follow-up, compare above all with the patient's own previous measurement.
How to read the result
Volume describes the gland, not its function. A normal volume does not exclude thyroiditis or a nodule, and an enlarged gland can be entirely euthyroid.
The formula
Lobe volume (mL) = length × width × depth × 0.479
Measure length on the longitudinal view and width and depth on the transverse view, in centimetres. The total is the sum of both lobes.
The isthmus is not included unless it is clearly thickened, in which case report it separately.
The coefficient 0.479 comes from the Brunn correction and runs slightly lower than the plain ellipsoid coefficient of π/6.
When to use it
- Reporting a thyroid ultrasound where the volume belongs in the conclusion.
- Documenting a goitre and its change over time.
- Planning radioiodine treatment or surgery, where the volume steers the dose or the approach.
- Comparing with an earlier study, where a consistent method matters more than the absolute value.
⚠️ Pitfalls
- Mixing planes is the commonest source of disagreement: length on longitudinal, width and depth on transverse.
- A substernal extension cannot be measured on ultrasound, so the reported volume underestimates a retrosternal goitre.
- Upper limits vary with iodine intake and between reference populations. Treat them as orientation.
- The formula assumes an ellipsoid lobe. A dominant nodule deforming the lobe makes the estimate drift.
- Volume does not grade nodules. A nodule in a normal-sized gland still needs its own TI-RADS assessment.
Frequently asked questions
What is the formula for thyroid volume?
Per lobe: length × width × depth × 0.479, with diameters in centimetres. The total volume is the sum of both lobes.
What is a normal thyroid volume?
Commonly used upper limits are around 18 mL in women and 25 mL in men, though these vary with iodine intake and reference population.
Is the isthmus included?
No. It is excluded unless clearly thickened, and even then it is better reported separately so measurements stay comparable over time.
Why 0.479 and not π/6?
0.479 is the Brunn correction, derived specifically for the thyroid. It sits slightly below the plain ellipsoid coefficient of about 0.524.
Does volume say anything about thyroid function?
No. An enlarged gland can be euthyroid and a normal-sized gland can be hypo- or hyperthyroid. Read the volume alongside the TSH.
References
📄Brunn J, et al. Volumetric analysis of thyroid lobes by real-time ultrasound. Dtsch Med Wochenschr. 1981;106(41):1338–1340.
📄WHO/ICCIDD. Recommended normative values for thyroid volume in ultrasonography.
This calculator supports clinical judgement and does not replace it. Always check the result against your own measurements and the guideline in force.
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