Educational tool — not a diagnosis. This applies a published formula to numbers you enter. Thyroid volume is interpreted by clinicians alongside symptoms, thyroid function tests, nodule findings and the local reference range.
Discuss any result with the healthcare professional who arranged your scan. Do not use this page to make decisions about tests or treatment.
Quick answer: each lobe is length × width × depth × 0.479, and the two are added for the total. A 4 × 2 × 2 cm lobe is 7.66 mL. The isthmus is normally excluded. Goitre is defined against the local reference range — commonly quoted as up to ~18 mL in women and ~25 mL in men.
Brunn's formula, and why 0.479
Total = right lobe + left lobe
Each thyroid lobe is modelled as an ellipsoid. The pure geometric coefficient would be π/6 ≈ 0.524, but Brunn and colleagues found in 1981 that a lower coefficient of 0.479 matched measured lobe volumes more closely — a thyroid lobe is a slightly slimmer ellipsoid than the geometry assumes. That empirically-derived 0.479 became the standard for thyroid ultrasound and is what this calculator uses.
Brunn J, Block U, Ruf G, et al. Volumetric analysis of thyroid lobes by real-time ultrasound. Deutsche Medizinische Wochenschrift, 1981;106:1338–1340. The coefficient 0.479 is applied to each lobe and the results summed.
Worked example — a right lobe of 4.5 × 1.8 × 2.0 cm and a left lobe of 4.2 × 1.6 × 1.9 cm:
- Right: 4.5 × 1.8 × 2.0 × 0.479 = 7.76 mL
- Left: 4.2 × 1.6 × 1.9 × 0.479 = 6.12 mL
- Total: 13.88 mL
Reference ranges
| Group | Commonly cited upper limit |
|---|---|
| Adult women | ≈ 18 mL |
| Adult men | ≈ 25 mL |
| Above the local upper limit | Described as goitre |
These are widely cited figures for iodine-sufficient adults, but reference ranges genuinely vary between populations, iodine intake and individual studies — and children have age- and body-size-dependent ranges. The threshold that matters for interpretation is the one used by the laboratory or guideline where the scan was reported, not a universal number.
Frequently asked questions
How is thyroid volume calculated?
Each lobe is measured separately with the ellipsoid formula using Brunn's coefficient: lobe volume = length × width × depth × 0.479. The two lobe volumes are added together for the total. The isthmus is usually excluded as its contribution is small. A lobe of 4 × 2 × 2 cm gives 4 × 2 × 2 × 0.479 = 7.66 mL.
What is a normal thyroid volume?
In iodine-sufficient adults, total thyroid volume is commonly cited as up to about 18 mL in women and up to about 25 mL in men, though reference ranges vary between populations and studies. Volume above the local upper limit is described as goitre. Children have smaller reference ranges that increase with age and body surface area.
What is Brunn's formula?
Brunn's formula, published in 1981, estimates each thyroid lobe as an ellipsoid using the coefficient 0.479 rather than the geometric π/6 of 0.524. The lower coefficient was derived empirically to better match measured thyroid lobe volumes, and it became the standard for thyroid ultrasound.
Should I include the isthmus?
Usually not. The standard method sums the two lobes and omits the isthmus, whose volume is small and difficult to measure reliably. Some protocols add it when it is notably enlarged, but for routine estimation the two-lobe sum is the convention.
How accurate is ultrasound thyroid volume?
It is an estimate that works well for regularly shaped lobes. Accuracy falls when the gland is multinodular or asymmetric, where the ellipsoid assumption breaks down and the method tends to overestimate. As with any three-diameter method, measurement errors compound because the diameters are multiplied together.
References
- Brunn J, Block U, Ruf G, et al. Volumetric analysis of thyroid lobes by real-time ultrasound. Deutsche Medizinische Wochenschrift, 1981;106:1338–1340.
- WHO/ICCIDD reference ranges for thyroid volume by ultrasound in iodine-sufficient populations.
- General references on goitre definition and population-specific thyroid volume reference ranges.