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Tree Diameter Calculator.

Convert a measured trunk circumference to diameter, radius, and basal area.

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Trunk circumference

Diameter

31.831cm

Radius

15.915cm

Basal area

795.775cm²

This page uses the explicit circumference method: diameter = circumference ÷ π. Measure around the same trunk point used for your field record.

Use Cases

Forestry and Timber Estimation

Quickly determine tree diameter and basal area for forest inventories, timber volume estimates, and ecological studies.

Example: Measure circumference of 150 cm to get diameter ≈ 47.75 cm and basal area ≈ 1790 cm².

Tree Health and Growth Monitoring

Track changes in tree diameter over time to assess growth rates and overall health.

Example: Record circumference annually and compare diameter changes.

Frequently Asked Questions

How do I calculate tree diameter from trunk circumference?: Divide the trunk circumference by π (pi, approximately 3.14159). The result is the tree diameter. For example, a circumference of 100 cm gives a diameter of about 31.83 cm.
What is basal area and how is it calculated?: Basal area is the cross-sectional area of the trunk at breast height, usually expressed in square centimeters. It is calculated using the formula: basal area = π × (diameter/2)², or equivalently, circumference² / (4π).
Why is tree diameter measured at breast height?: Measuring at breast height (about 1.3 m above ground) provides a standardized and consistent point for comparison. This calculator uses the trunk circumference you input, which is typically measured at that height.

Tips & Common Mistakes

Tips

Measure circumference at a consistent height (usually 1.3 m) for accurate comparisons.
Use a flexible measuring tape and ensure it is snug but not compressing the bark.
For irregular trunks, measure at the narrowest point below any swelling or branch.
Double-check your circumference input to avoid errors in diameter and basal area calculations.

Common Mistakes to Avoid

Using diameter instead of circumference as input – the calculator expects trunk circumference.
Measuring at different heights each time, leading to inconsistent results.
Forgetting to convert units – ensure circumference is in centimeters as specified.

Last updated: August 13, 2026

Use Cases

Forestry and Timber Estimation

Quickly determine tree diameter and basal area for forest inventories, timber volume estimates, and ecological studies.

Example: Measure circumference of 150 cm to get diameter ≈ 47.75 cm and basal area ≈ 1790 cm².

Tree Health and Growth Monitoring

Track changes in tree diameter over time to assess growth rates and overall health.

Example: Record circumference annually and compare diameter changes.

Frequently Asked Questions

How do I calculate tree diameter from trunk circumference?

Divide the trunk circumference by π (pi, approximately 3.14159). The result is the tree diameter. For example, a circumference of 100 cm gives a diameter of about 31.83 cm.

What is basal area and how is it calculated?

Basal area is the cross-sectional area of the trunk at breast height, usually expressed in square centimeters. It is calculated using the formula: basal area = π × (diameter/2)², or equivalently, circumference² / (4π).

Why is tree diameter measured at breast height?

Measuring at breast height (about 1.3 m above ground) provides a standardized and consistent point for comparison. This calculator uses the trunk circumference you input, which is typically measured at that height.

Tips & Common Mistakes

Tips

Measure circumference at a consistent height (usually 1.3 m) for accurate comparisons.
Use a flexible measuring tape and ensure it is snug but not compressing the bark.
For irregular trunks, measure at the narrowest point below any swelling or branch.
Double-check your circumference input to avoid errors in diameter and basal area calculations.

Common Mistakes to Avoid

Using diameter instead of circumference as input – the calculator expects trunk circumference.
Measuring at different heights each time, leading to inconsistent results.
Forgetting to convert units – ensure circumference is in centimeters as specified.

Use Cases

Forestry and Timber Estimation

Quickly determine tree diameter and basal area for forest inventories, timber volume estimates, and ecological studies.

Example: Measure circumference of 150 cm to get diameter ≈ 47.75 cm and basal area ≈ 1790 cm².

Tree Health and Growth Monitoring

Track changes in tree diameter over time to assess growth rates and overall health.

Example: Record circumference annually and compare diameter changes.

Frequently Asked Questions

How do I calculate tree diameter from trunk circumference?

Divide the trunk circumference by π (pi, approximately 3.14159). The result is the tree diameter. For example, a circumference of 100 cm gives a diameter of about 31.83 cm.

What is basal area and how is it calculated?

Why is tree diameter measured at breast height?

Tips & Common Mistakes

Tips

Measure circumference at a consistent height (usually 1.3 m) for accurate comparisons.
Use a flexible measuring tape and ensure it is snug but not compressing the bark.
For irregular trunks, measure at the narrowest point below any swelling or branch.
Double-check your circumference input to avoid errors in diameter and basal area calculations.

Common Mistakes to Avoid

Using diameter instead of circumference as input – the calculator expects trunk circumference.
Measuring at different heights each time, leading to inconsistent results.
Forgetting to convert units – ensure circumference is in centimeters as specified.