Biology
Turn a trunk circumference measured at breast height into diameter (DBH).
Your inputs
Change any value — everything updates instantly.
Wrap a tape around the trunk 4.5 ft (1.37 m) above the ground.
Try an example
Diameter (DBH)
19.1 in
This means the trunk is about 19.1 in (48.5 cm) across.
What you are seeing
The blue line traces the tape around the trunk.
The green line is the diameter straight across.
60 in around gives 19.1 in across.
Centimetres
48.5 cm
Diameter in metric.
Radius
9.55 in
Half the diameter.
Result explanation: Trunk diameter
19.1 in DBH.
Real-life comparison: Adding 10 in of circumference adds 3.18 in of diameter.
Low, normal or high? A medium-sized trunk.
Diameter against circumference
How to read this chart: Diameter grows in a straight line with circumference. The dot is your tree.
Divides the measured circumference by π to get the diameter.
DBH is 19.1 in.
DBH is the standard size used in forestry and tree care.
Use it in basal area and tree age tools.
Circumference divided by π.
DBH = C ÷ π
Symbols
Why this formula works
A circle's circumference is π times its diameter.
Unit check
in ÷ number = in ✓
Worked example
Common mistakes
The trunk diameter is 19.1 in.
It is the standard breast height used in the US so measurements can be compared.
Measure each stem separately just above the fork.
Yes — a D-tape is printed to read diameter directly.
Measure 4.5 ft up from the uphill side.
Important limitation. Oval or fluted trunks give an average diameter only.
Tell us if a formula, unit, explanation, or result needs attention. Your message will include this calculator’s name and page.
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