Tree Girth to Diameter: The Circular Cross-Section Assumption Is Explicit; illustrative quantitative diagram
Define the quantity before calculating
A tape measures circumference around a cross-section; division by pi gives a circular-equivalent diameter. An irregular cross-section does not become circular because the formula is used. Keep the measuring method with the result.
Use Tree Diameter Calculator with the units and the basis stated on its form. Check what each input represents before carrying the output into another record.
Read the model explicitly
Circular-equivalent diameter cm = circumference cm / π.
The Trees & Forestry Calculators group sits within Biology calculators. Keep a measured observation distinguishable from a hypothetical input when moving between its tools.
A worked unit check
| Input as labeled on the tool | Illustrative value |
|---|---|
| Circumference at the recorded measurement height (cm) | 100 |
| Output from the illustrative inputs | Value | Unit |
|---|---|---|
| Circular-equivalent diameter | 31.831 | cm |
Record the original input and its unit with this result. Recalculate when the measurement basis changes; changing a unit label after calculation does not convert the quantity. More decimal places do not remove sampling or measurement uncertainty.
A related quantity
Basal Area Calculator addresses a related part of the task. Check its own input definition before carrying a number across.
Continue with Record Measurement Height Before Comparing Trunk Diameters for the other part of this measurement question.
Return to GreenCalc for other subjects. Keep raw observations, chosen assumptions and calculated quantities identifiable so a later revision does not overwrite the basis of the original record.
By GreenCalc · Updated 2026-11-06