Tree Diameter Calculator

Calculate a tree's diameter from circumference, with bark thickness adjustments.

Supports single and multi-stemmed trees with metric and imperial units.

Updated July 29, 2026

CreatorFrank Zhao

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Introduction / overview

The Tree Diameter Calculator lets you estimate the diameter of a tree trunk from its circumference — the measurement you can easily take with a simple measuring tape. Whether you're dealing with a classic single-trunk tree or a multi-stemmed specimen with several stems branching near the ground, this tool handles both situations and also accounts for bark thickness to give you the diameter of the wood inside.

Tree diameter at breast height (DBH) is the universal standard measurement used by foresters, arborists, ecologists, and tree enthusiasts. It's the foundation for estimating tree age, wood volume, biomass, carbon storage, growth rate, and even tree value. Instead of reaching for a cumbersome tree caliper or doing the math by hand, just wrap a tape around the trunk and let the calculator do the rest.

✅ Whether you're a homeowner curious about your backyard oak, a student learning forest mensuration, or a professional conducting a tree inventory — this calculator gives you quick, accurate diameter readings from a single circumference measurement.

Who is this for?

Homeowners and gardeners measuring trees on their property.
Arborists, foresters, and land managers conducting tree surveys.
Students and researchers in forestry, ecology, and environmental science.
Anyone who wants to estimate tree size for tree value, spacing, or planting decisions.

Once you have the diameter, you can go further — estimate the value of your tree, figure out how many trees fit in your land with the Tree Spacing Calculator, or measure its height with the Tree Height Calculator.

How to use / quick start

Getting your tree's diameter takes just a couple of steps. Here's the quickest path for a standard single-trunk tree.

1Measure the circumference of the trunk at breast height — that's about $1.35\ \mathrm{m}$ (or $4.5\ \mathrm{ft}$ ) above ground. Use a flexible measuring tape and wrap it snugly around the bark.
2Select your unit in the calculator — centimeters, inches, or feet. The composite units (ft/in or m/cm) let you enter values in feet and inches separately.
3Enter the circumference in the Circumference field. The Diameter field instantly shows the result. Change any unit and the value updates automatically.
4Optional: expand "Bark details" to enter bark thickness and get the under-bark (wood-only) diameter. If you don't know the bark thickness, just leave it blank — the over-bark diameter is already there.
5For multi-stemmed trees, switch to the Multi-stemmed tree section and enter the circumference of up to 6 stems. Leave unused stems at zero.

Worked example — single oak tree

You measure the circumference of a mature oak at chest height and get 120 cm.

1. Select "cm" as the unit for Circumference (it's already the default).
2. Type $120$ into the Circumference field.
3. The Diameter field reads ~38.2 cm — that's your tree's diameter at breast height.

d = \frac{C}{\pi}

=

\frac{120\ \mathrm{cm}}{\pi}

\approx

38.2\ \mathrm{cm}

If you want the diameter of the wood alone, open Bark details (single), enter the average bark thickness (say 2 cm), and the under-bark diameter reads ~34.2 cm.

How to interpret results

The Diameter (over-bark) is the trunk's full width including bark — what you'd measure with a caliper.
The Diameter under-bark is the wood-only diameter — useful for timber volume estimation and growth studies.
The Multi-stemmed diameter combines all stems into a single equivalent diameter using the root-sum-square method.

Real-world examples

Urban tree inventory — single sycamore

A city arborist needs to record the DBH of a mature sycamore growing along a downtown street. Using a measuring tape at $1.35\ \mathrm{m}$ above ground, they get a circumference of 187 cm. The tree has thick, flaky bark — the arborist estimates an average bark thickness of 3 cm.

d = \frac{C}{\pi}

=

\frac{187}{\pi}

\approx

59.5\ \mathrm{cm}

d_{\mathrm{ub}} = d - 2 \times BT

=

59.5 - 6

=

53.5\ \mathrm{cm}

Result: DBH over-bark is 59.5 cm, under-bark is 53.5 cm. This data goes into the city's tree management system, helping plan pruning cycles, sidewalk repair, and replacement schedules. The over-bark diameter can also be used with the Tree Value Calculator for a quick compensation estimate.

Multi-stemmed birch in a woodland

A birch tree in a forest copice has three main stems branching close to the ground. The forester measures each stem's circumference at breast height:

Stem 1: 65 cm
Stem 2: 52 cm
Stem 3: 31 cm

Entering these into the Multi-stemmed tree section (leaving stems 4–6 at zero) gives:

d_{ms} = \frac{1}{\pi}\sqrt{C_1^2 + C_2^2 + C_3^2}

= \frac{1}{\pi}\sqrt{65^2 + 52^2 + 31^2}

=

\frac{\sqrt{7890}}{\pi}

\approx

28.3\ \mathrm{cm}

Result: The multi-stemmed birch has an equivalent DBH of 28.3 cm. This combined diameter is used by foresters to estimate the tree's total wood volume and biomass, treating the multi-stemmed specimen as a single tree in yield models.

Thick-barked tree — bark adjustment in practice

A cork oak has a circumference of 250 cm and a very thick bark averaging 8 cm. The over-bark diameter is:

d = \frac{250}{\pi} \approx 79.6\ \mathrm{cm}

But the wood inside is significantly smaller:

d_{\mathrm{ub}} = 79.6 - 2 \times 8 = 63.6\ \mathrm{cm}

Result: The over-bark diameter of 79.6 cm would overestimate the actual wood volume by a significant margin. The under-bark measurement of 63.6 cm gives a more accurate picture for timber valuation. Bark thickness adjustments are especially important for species with thick, rough bark — like cork oak, redwood, or old-growth pine.

Common scenarios

The Tree Diameter Calculator fits into many real-world situations. Here are some of the most common ones.

Property tree valuation

Real estate appraisals often factor in the size and condition of mature trees. DBH is the key metric used in tree valuation formulas like the Council of Tree and Landscape Appraisers (CTLA) trunk formula method. Once you have the diameter, pair it with the Tree Value Calculator to estimate monetary value.

Growth & yield monitoring

Foresters measure DBH annually or periodically to track tree growth. A consistent increase in diameter over time indicates healthy growth. The calculator's ability to work with different units (cm, inches, ft) makes it easy to compare measurements taken with different tools or by different teams.

Tree planting & spacing design

When planning a new orchard or woodland, knowing the expected trunk diameter at maturity helps determine planting distances. Use the DBH in combination with the Tree Spacing Calculator to ensure each tree has enough room to develop a full canopy and root system. The multi-stemmed mode also applies to coppice or multi-trunk ornamental species.

Timber & biomass estimation

The wood industry relies on DBH to estimate timber volume using allometric equations. The under-bark diameter is especially important here — bark doesn't count as merchantable wood. The calculator's bark adjustment gives you both values, letting you compare gross and net volume estimates. For more precise wood volume, consider the tree's height as well using the Tree Height Calculator.

Tips & best practices

Getting the most accurate results

Measure at the right height. Standard DBH height varies by country: $1.35\ \mathrm{m}$ in Europe/Canada/Australia, $4.5\ \mathrm{ft}$ ( $1.37\ \mathrm{m}$ ) in the US, and $1.2\ \mathrm{m}$ in Japan/Korea. Always note which standard you're using.
On a slope, measure from the uphill side. Stand on the uphill side of the tree and measure at the standard height from the highest ground contact point. This compensates for the slope and gives a consistent reference.
For leaning trees, measure along the underside. Wrap the tape along the underside face of the trunk at breast height — this follows the natural curve of the tree and gives the most representative circumference.
Estimate bark thickness carefully. If you need under-bark diameter but can't measure bark thickness directly, consult species-specific references. Using an overestimated bark thickness can make the under-bark diameter negative (the calculator will warn you).
Dealing with irregularities. If the trunk has a bump, branch, or burl at breast height, measure slightly above or below the irregularity where the trunk is more uniform, then note the measurement height.
Multi-stemmed trees. Only combine stems if the point of separation is below ground (i.e., stems share a common root system but are separate above ground). If stems branch above ground, measure the largest stem individually — the calculator's single-stemmed mode is more appropriate.

Common mistakes to avoid

Measuring too low or too high. A measurement at ground level (root collar) can be much wider than DBH, dramatically overestimating the tree's true diameter.
Confusing diameter with circumference. A common slip — entering the circumference in the diameter field or vice versa. The calculator's smart bidirectional engine will still work, but the result will be wrong. Double-check which measurement you've taken.
Mixing units incorrectly. If you measure in inches but leave the calculator set to centimeters, the result will be off by a factor of about 2.54. Always check the unit selector matches your tape measure.

Calculation method / formulas

The Tree Diameter Calculator relies on three core formulas. All of them are derived from the fundamental relationship between a circle's circumference and its diameter — because a tree trunk cross-section is approximated as a circle.

Formula 1 — Single-stemmed diameter (over-bark)

This is the basic circumference-to-diameter conversion, using the classic circle formula:

d = \frac{C}{\pi}

Where $C$ is the circumference and $\pi \approx 3.1416$ .

Reverse direction:

If you already know the diameter, you can find the circumference by simply reversing the formula:

C = \pi \times d

Formula 2 — Under-bark diameter (single-stemmed)

To get the diameter of the wood alone, subtract twice the bark thickness from the over-bark diameter:

DUB = DOB - 2 \times BT

Where $DOB$ is the diameter over-bark and $BT$ is the average bark thickness.

What you can calculate from this formula:

Over-bark diameter from under-bark diameter and bark thickness: $DOB = DUB + 2 \times BT$
Bark thickness from over-bark and under-bark diameters: $BT = \frac{DOB - DUB}{2}$

Formula 3 — Multi-stemmed tree diameter

For multi-stemmed trees, the calculator first converts each stem's circumference to its individual diameter, squares them, sums them up, and takes the square root. This is the "root-sum-square" method:

d_{ms} = \frac{1}{\pi} \sqrt{\sum_{i=1}^{6} C_i^2}

Where $C_i$ is the circumference of the $i$ -th stem.

How to find the diameter of a multi-stemmed tree step by step:

Measure the circumference of each stem at breast height (up to 6 stems).
Convert each circumference to diameter: $d_i = C_i / \pi$
Square each diameter: $d_i^2$
Add all the squares together.
Take the square root of the sum.

d_{ms} = \sqrt{d_1^2 + d_2^2 + \cdots + d_6^2}

Formula 4 — Multi-stemmed under-bark diameter

This is a read-only output based on the largest stem's diameter and the multi-stemmed bark thickness. If the first stem is zero or its radius is smaller than the bark thickness, the result is zero — otherwise it's the first stem's under-bark diameter:

d_{ms,ub} = \max\!\left(0,\ \frac{C_1}{\pi} - 2 \times BT_m\right)

Where $C_1$ is the first (largest) stem's circumference and $BT_m$ is the average bark thickness for multi-stemmed trees. This field is read-only because it combines data from two separate input sources.

Related concepts & background

What is DBH (Diameter at Breast Height)?

DBH is the standard way to measure tree trunk diameter, taken at a fixed height above ground. The exact height varies by region — $1.35\ \mathrm{m}$ in most of the world, $4.5\ \mathrm{ft}$ ( $1.37\ \mathrm{m}$ ) in the United States, and $1.2\ \mathrm{m}$ in Japan and Korea. DBH is the foundation of forest mensuration — nearly every allometric equation for tree biomass, volume, and growth uses DBH as the primary input.

Why bark thickness matters

Bark can account for 5-25% of a tree's diameter, depending on species and age. Species like cork oak, redwood, and certain pines have very thick bark that can significantly inflate the over-bark diameter. When estimating timber volume, carbon content, or growth rates, using the under-bark diameter gives a more accurate picture of the actual wood produced. The calculator's bark adjustment lets you easily compare both values.

Single-stemmed vs multi-stemmed trees

Not all trees grow with a single, straight trunk. Many species — especially birches, willows, and some ornamentals — produce multiple stems from a common root system. The standard forestry practice is:

If the stems separate below ground, treat each one as a separate tree and measure its DBH individually.
If the stems separate above ground, treat the plant as a single multi-stemmed tree. The root-sum-square method gives an equivalent diameter that represents the combined stem area.

This distinction is important for accurate carbon accounting, timber valuation, and growth modeling.

From diameter to other tree measurements

Once you have the DBH, you can estimate a surprising amount of information about a tree:

Tree value — combined with height and species, DBH is the main input for tree appraisal. Use the Tree Value Calculator for a quick estimate.
Tree height — diameter and height together give a more complete picture of tree size. The Tree Height Calculator can help with that.
Planting density — knowing the mature diameter helps plan proper spacing. Try the Tree Spacing Calculator to optimize your planting layout.

Frequently asked questions

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

Measure the circumference at breast height on the uphill side of the tree. This means you stand uphill and measure at $1.35\ \mathrm{m}$ (or $4.5\ \mathrm{ft}$ ) from the highest point of ground contact. This standard method ensures consistency regardless of slope angle.

How do I measure a leaning tree?

Wrap the measuring tape around the leaning tree at breast height, following the underside face of the trunk. This follows the natural curve and gives the most representative circumference measurement. Then divide by $\pi$ as usual.

How much does a tree grow in diameter each year?

Most temperate trees grow between 0.2 cm and 0.4 cm in diameter per year, which corresponds to roughly 1.5 cm to 2.5 cm in circumference growth. Growth rates vary widely by species, age, site conditions, climate, and competition. Fast-growing species like poplar or eucalyptus can add $1-3\ \mathrm{cm}$ of diameter per year, while slow-growing oaks and beeches may only add a few millimeters.

How do I estimate the diameter of a tree stump?

For a cut stump, measure the widest diameter and the narrowest diameter across the cut surface, then take the average. Place your measuring tape directly on the ground beside the stump for width measurements. Note that stump diameter is usually larger than the tree's DBH was, because stumps are measured near ground level where trunks are wider.

Can I calculate circumference from diameter?

Yes! Just enter the diameter and the calculator automatically shows the corresponding circumference. The relationship works both ways — that's the beauty of the simple circle formula: $C = \pi \times d$ .

Does the calculator work for saplings and very small trees?

Yes — the formulas work at any scale. However, for very small trees (diameter under $2-3\ \mathrm{cm}$ ), measuring circumference accurately with a standard tape can be tricky. You may get more precise results using a caliper or a diameter tape (d-tape) directly. The calculator also requires circumference to be greater than zero for single-stemmed trees.

Limitations & disclaimers

The Tree Diameter Calculator provides a quick, mathematical conversion from circumference to diameter assuming a perfectly circular trunk cross-section. In reality, tree trunks are rarely perfect circles — they can be oval, irregular, or tapered. The results are therefore estimates and should be treated as such.

Important considerations:

Measurement accuracy depends on you. The calculator can only be as accurate as the measurements you put in. A loose tape, wrong height, or misread value will produce misleading results. Take multiple measurements and average them for best accuracy.
Bark thickness is an estimate. Unless you're measuring a freshly cut stump or using a bark gauge, bark thickness is typically estimated from species averages. Actual bark thickness varies around the trunk and with tree age.
Multi-stemmed diameter is a derived value. The root-sum-square method gives an equivalent diameter that represents the combined cross-sectional area of all stems. It does not directly correspond to a physical single-stem diameter and should be used with that context in mind.
Not a substitute for professional assessment. For tree valuation, timber sales, hazard assessment, or legal purposes, always consult a certified arborist, professional forester, or qualified tree appraiser. This calculator is a planning and educational tool.
Regional standards vary. The calculator uses the standard DBH height for your convenience, but always verify which measurement protocol applies in your region or for your specific purpose.

Note: The formulas used in this calculator are based on standard geometric relationships and forestry practices. They are provided for educational and estimation purposes. Always verify critical measurements with appropriate field equipment and consult relevant forestry or arboricultural standards for your specific application.

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