Lung Nodule Growth Rate Calculator — Volume Doubling Time
Enter the nodule diameter on two CT scans and the days between them to compute the Volume Doubling Time (VDT) — the key metric used by radiologists and pulmonologists to assess whether a lung nodule is more likely benign or malignant.
mm
mm
days
Time for the nodule volume to double (assuming spherical shape)
- 1
Diameter ratio
8 ÷ 6 = 1.3333 - 2
ln(d₂ / d₁)
ln(1.3333) = 0.287682 - 3
Volume Doubling Time
90 × ln(2) ÷ (3 × 0.287682) = 72VDT = t × ln(2) / (3 × ln(d₂/d₁)); assumes spherical nodule (V ∝ d³).
How does this calculator work?
VDT = t × ln(2) / (3 × ln(d₂/d₁)) where t is days between scans and d₁, d₂ are nodule diameters. VDT < 400 days is suspicious for malignancy; VDT > 600 days is likely benign. This is an educational reference — nodule management always requires specialist input.
Formula
How this is calculated
A pulmonary nodule's growth rate is one of the strongest predictors of malignancy. The Volume Doubling Time (VDT) is the number of days it takes the nodule's volume to double. Because volume scales as diameter cubed (assuming a sphere), doubling the volume corresponds to only a 26% increase in diameter — so diameter changes alone can be misleading without this calculation.
The formula derives from logarithms: ln(V₂/V₁) = ln((d₂/d₁)³) = 3·ln(d₂/d₁). Setting V₂ = 2·V₁ and solving for time gives VDT = t·ln(2) / (3·ln(d₂/d₁)), where t is the time between scans in days and d₁, d₂ are the diameters at each scan.
Fleischner Society and Lung-RADS guidelines use VDT thresholds to guide management. A VDT shorter than 400 days is considered suspicious for malignancy; values between 400–600 days are indeterminate; values greater than 600 days are generally reassuring. Very fast growth (VDT < 20 days) often indicates an infectious or inflammatory process rather than a slow-growing carcinoma. These thresholds are guidelines only — nodule size, morphology, patient risk factors, and clinical context all influence the management decision, which must involve a specialist.
Frequently asked questions
Volume scales as diameter cubed, so a nodule can nearly double in volume with only a modest increase in diameter. VDT captures true volumetric growth and is a stronger predictor of malignancy than simple size change. A 26% diameter increase already represents a volume doubling.
Fleischner Society guidance considers a VDT under 400 days suspicious for malignancy, 400–600 days indeterminate, and over 600 days likely benign. Very rapid growth (VDT under 20 days) often suggests infection or inflammation rather than carcinoma.
No. Nodule management decisions depend on size, morphology (solid vs. sub-solid), patient risk factors, and clinical context — not VDT alone. Always have CT findings reviewed by a qualified radiologist and follow institutional or Fleischner Society guidelines.
Also known as
TG we-Calculate Editorial Team. (2026). Lung Nodule Growth Rate Calculator — Volume Doubling Time [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/lung-nodule-growth-rate-calculator
TG we-Calculate Editorial Team. "Lung Nodule Growth Rate Calculator — Volume Doubling Time." TG we-Calculate. 2026. https://we-calculate.com/calculator/lung-nodule-growth-rate-calculator.
TG we-Calculate Editorial Team, "Lung Nodule Growth Rate Calculator — Volume Doubling Time," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/lung-nodule-growth-rate-calculator
@misc{wecalculate_lung_nodule_growth_rate_calculator, title = {Lung Nodule Growth Rate Calculator — Volume Doubling Time}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/lung-nodule-growth-rate-calculator}}, year = {2026}, note = {TG we-Calculate} }
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