# Lung Nodule Growth Rate Calculator (Volume Doubling Time)

URL: https://speedycalculator.com/calculators/health/lung-nodule-growth-rate/
Last updated: 2026-10-30

> The lung nodule growth calculator estimates the volume doubling time of a pulmonary nodule from its diameter (or volume) on two CT scans and the time between them – a key clue to whether a nodule is benign or malignant.

## Inputs

- First diameter (mm)
- Second diameter (mm)
- Days between scans

## Results

- First volume
- Second volume
- Volume change
- Volume doubling time

## Formula

```
Volume = π/6 × diameter³
Volume doubling time (days) = days × ln 2 ÷ ln(V₂ ÷ V₁)
< 400 days: suspicious for malignancy · 400–600 indeterminate · > 600 days usually benign
```

## Explanation

Most lung cancers double in volume within 20–400 days. Very fast growth (under 20 days) suggests infection, while no growth over 2 years for a solid nodule usually indicates a benign lesion. Volumetry is more precise than diameter.

### How to use the Lung Nodule Growth Rate Calculator

- **First diameter**
- **Second diameter**
- **Days between scans**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the average nodule diameter on each scan and the days between them.

### Inputs explained

FieldWhat to enterFirst diameterIn mmSecond diameterIn mmDays between scansA number

### What each result means

- **First volume** = pi÷6×[First diameter]^3
- **Second volume** = pi÷6×[Second diameter]^3
- **Volume change** = ([Second volume]÷[First volume] - 1)×100

*Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.*

## Worked example

Inputs — First diameter: 6 mm; Second diameter: 7.5 mm; Days between scans: 120.

Results — First volume = 113 mm³; Second volume = 221 mm³; Volume change = 95 %; **Volume doubling time = 124 days**.

## Key terms

- **VDT**: Volume doubling time.

## FAQ

**What doubling time suggests cancer?**
20–400 days for solid nodules.

**Why use volume rather than diameter?**
A 26% increase in diameter already doubles the volume.

**What if the nodule shrinks?**
Shrinking nodules are usually inflammatory or infectious.


## Sources

- [MacMahon H et al. Fleischner Society guidelines for incidental pulmonary nodules, 2017. Radiology](https://pubmed.ncbi.nlm.nih.gov/28240562/)