With a simple measuring tape and our tree diameter calculator, you can easily estimate the diameter of a tree - diameter at breast height (DBH).

Using this tree diameter calculator, you can estimate the trunk’s diameter of single and multi-stemmed trees on level ground or a slope. You can also find the diameter of a leaning tree using our tool!

🙋 We use the diameter of a tree to estimate its size and volume, growth and calculate its fertilizer requirements, the potential tree value as a source of wood or biomass, and its carbon storage.

🙋 What is the tree value? Learn it with Omni's tree value calculator!

How to calculate the diameter of a tree - dbh

We measure the circumference and diameter of a tree at "breast height". We call these measurements the circumference at breast height (CBH) and diameter at breast height (DBH) of trees.

🙋 Do you know that DBH height varies for different countries? If you are estimating DBH for trees in Australia, Canada, and Europe, measure it at 1.3 m1.3\ \text{m} (4.27 ft4.27\ \text{ft}) above ground level. In Japan and Korea, measure it at 1.2 m1.2\ \text{m} (3.93 ft3.93\ \text{ft}). In New Zealand, measure DBH at 1.4 m1.4\ \text{m} (4.59 ft4.59\ \text{ft}), and in the United States at 4.5 ft4.5\ \text{ft} (1.37 m1.37\ \text{m}).

To estimate the diameter of a tree:

  1. Wrap a tape tightly around the tree trunk at the DBH height - for example, at 4.5 feet in the US.
  2. Now, find where the number “0” on your tape aligns with the rest of the tape. This number is the circumference of the trunk.
  3. Find the diameter using the formula:
d=Cπd = \frac{C}{\pi}

Where:

  • dd — The diameter;
  • CC — The circumference; and
  • π\pi — The best mathematical constant, pi!

This is one of the most simple yet important relationships in math: discover it with our circle calculator!

How to use the tree diameter calculator

Follow these steps to quickly find the diameter of your tree using our calculator:

  1. Select the unit of length from the drop-down list beside the circumference box.
  2. Enter the value of the circumference you measured at the DBH height.
  3. Read the diameter of the tree from the second field.
  4. You can switch the unit of the diameter if you wish, maybe with our length converter.

🙋 You can calculate the circumference of the tree from the diameter by using our tree diameter calculator in reverse!

How do you find the diameter of the wood inside the bark?

The diameter we measure outside the bark is the diameter over-bark or diameter outside-bark. The diameter under-bark or diameter inside-bark is the diameter of the wood inside the bark of a tree.

To calculate the diameter of the wood inside the bark, subtract twice the average bark thickness from the diameter over-bark:

  • DUB = DOB - (2 * BT)

where:

  • DUB - Diameter under-bark;
  • DOB - Diameter over-bark; and
  • BT - Average bark thickness.

You can just switch to the advanced mode of our tree diameter calculator to find the diameter under-bark of a tree!

How do I calculate the diameter of a tree on a slope?

To find the diameter of a tree on a slope:

  1. Measure the circumference of the tree at breast height (usually, 1.35 m from the ground) on its uphill side.
  2. Divide the tree circumference by π (= 3.14) to estimate your tree's diameter at breast height (DBH) on a slope.

How do I measure the circumference of a leaning tree on level ground?

Measuring the circumference of a leaning tree is not a difficult task. Wrap the measuring tape around the leaning tree at breast height (about 1.35 m from the ground) along the underside face of the trunk to measure its circumference.

Divide the tree circumference by π (= 3.14) if you want to find the diameter of your leaning tree.

How do I calculate the diameter of a multi-stemmed tree?

Consider each stem as a separate tree, if the pith union is below ground, i.e., the stems are from a common rootstock and are not connected above the ground. So, determine the diameter at breast height (DBH) for each stem separately.

Consider the plant as a single tree, if the point of pith separation is above ground. Then, to find the diameter of such a tree:

  1. Measure the circumference of the six largest stems.
  2. Calculate the diameter of each stem. To check your results, use the tree diameter calculator.
  3. Find the square of each value of diameter.
  4. Add the squares.
  5. Find the square root of the sum. Congratulations! You've now found the diameter of your multi-stemmed tree.

With our tree diameter calculator, you can find the diameter of a multi-stemmed tree both outside and inside the bark (use the advanced mode for bark calculations). Let's try it!

FAQ

How do I measure the diameter of a tree stump?

The average width of a wider side and a narrow side gives you the stump's diameter. Measure the width by placing the measuring tape beside the stump on the ground.

How much does a tree grow in diameter per year?

Most trees grow between 0.2 cm and 0.4 cm in diameter and between 1.5 cm and 2.5 cm in circumference per year.

How do I calculate my 10 year-old oak tree's circumference without a tape?

To find 10 year-old oak tree's circumference:

  1. Multiply a tree's age (in years) with 2.5 to find its circumference in centimeters:
    • circumference (in cm) = 2.5 x age (in years)
  2. So, your oak tree should have a circumference of 25 cm.
  3. Divide the circumference by 3.14 if you want to find the diameter: 7.96 cm.

Every 2.5 cm of girth represents about one year's growth. So by multiplying a tree's age by 2.5 (in some cases, 1.5 or 2) you can roughly estimate a tree's circumference. This method is known as Mitchell’s Rule.

How do I calculate the diameter of a tree of circumference 40 cm?

Divide the tree circumference by π (= 3.14) to find the diameter. So, your tree has a diameter of 12.7 cm.

Mehjabin Abdurrazaque
Single-stemmed tree
Circumference
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Diameter
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Multi-stemmed tree (leave zero if you have less stems)
First stem circumference
in
Second stem circumference
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Third stem circumference
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Fourth stem circumference
in
Fifth stem circumference
in
Sixth stem circumference
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Diameter
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