DBH Calculator (Tree Diameter Calculator)

What Is DBH (Diameter at Breast Height)?

DBH, or Diameter at Breast Height, is the standard method used by arborists, foresters, municipalities, and tree care professionals to measure tree size. The measurement is taken 4.5 feet above ground level on the uphill side of the trunk, providing a consistent way to compare trees regardless of species or growing conditions. In some regions and municipal codes, DBH may also be referred to as DSH (Diameter at Standard Height), though both terms generally refer to the same standardized trunk measurement. In some municipalities and tree protection ordinances, DBH is also referred to as DSH (Diameter at Standard Height)

Tree diameter measurements play an important role in arboriculture, urban forestry, and land development. Cities and counties often use DBH or DSH thresholds to determine whether a tree qualifies as significant, exceptional, protected, or subject to permit requirements. Arborists also use DBH measurements when performing tree inventories, risk assessments, appraisals, construction planning, and arborist reports.

Because measuring diameter directly can be difficult on large trees, DBH is commonly calculated by measuring the tree's circumference with a tape measure and converting that measurement into diameter. Our free DBH Calculator makes the process quick and accurate, helping homeowners, property managers, developers, and arborists determine tree size in seconds.

Why Tree Diameter Matters

Determining a tree's diameter is important for permit compliance, arborist reports, tree inventories, and property development projects. Diameter at Breast Height (DBH) is the standard measurement used by municipalities, arborists, foresters, and land-use professionals to evaluate tree size and determine whether a tree qualifies as significant, protected, exceptional, or subject to removal regulations.

• Tree Removal Permits: Many cities use DBH thresholds to determine when permits, arborist reports, or replacement plantings are required.
• Significant Tree Determinations: Local tree protection ordinances often classify trees based on their diameter, making accurate measurements essential for compliance.
• Arborist Reports and Tree Risk Assessments: ISA Certified Arborists use DBH measurements when evaluating tree condition, risk, preservation potential, and management recommendations.
• Development and Construction Projects: Tree diameter is commonly used when preparing tree retention plans, site development permits, critical area reports, and construction impact assessments.
• Tree Appraisals and Valuations: DBH is a key factor used to estimate tree value, replacement cost, and landscape asset worth.

Whether you're applying for a permit, planning construction, or simply trying to understand the size of a tree on your property, accurately measuring DBH is often the first step.

How to Measure DBH (Diameter at Breast Height)

Measuring a tree's Diameter at Breast Height (DBH) is simple and only requires a tape measure. First, locate a point 4.5 feet above ground level on the uphill side of the tree. At this height, wrap a flexible tape measure completely around the trunk and record the circumference in inches. Enter that measurement into the DBH Calculator above to instantly determine the tree's diameter.

For most single-stem trees, this measurement provides an accurate representation of tree size and is the standard method used by arborists, foresters, municipalities, and permitting agencies. If the tree has multiple stems, unusual trunk flare, or significant deformities at breast height, additional measurement techniques may be required. Multi-stem trees are often calculated using specialized formulas that vary by jurisdiction and intended use.

Accurate DBH measurements are important for tree inventories, arborist reports, permit applications, development projects, tree appraisals, and determining whether a tree meets local significant tree or protected tree thresholds. Using a standardized measurement height ensures consistency across inspections, regulations, and professional assessments.

Quick Steps for Measuring DBH

1. Locate 4.5 feet above ground level on the uphill side of the tree.
2. Wrap a tape measure around the trunk at that height.
3. Record the circumference in inches.
4. Enter the measurement into the calculator to determine the tree's DBH.

Tip: If the tree has multiple trunks, significant buttress roots, or an irregular stem shape, consult the multi-stem calculation guidance below or contact an ISA Certified Arborist for assistance.

How to Convert Circumference to DBH

A tree's diameter can be calculated by dividing its circumference by pi (3.1416). Simply measure the trunk circumference at breast height using a tape measure and enter the value into the calculator above. The calculator will automatically convert the measurement into Diameter at Breast Height (DBH), the standard tree sizing method used by arborists, foresters, and municipalities throughout North America.

Multi-Stem Tree DBH Calculations

Calculating the Diameter at Breast Height (DBH) of a multi-stem tree is more complex than measuring a single trunk. Unlike single-stem trees, there is no universally accepted method for combining multiple stems into a single diameter measurement. Different cities, municipalities, forestry agencies, and arborists may use different calculation methods depending on the purpose of the measurement and local regulations.

In the Seattle area, arborists and many local jurisdictions commonly use the quadratic diameter method for multi-stem trees. This approach accounts for the cross-sectional area of each stem and provides a more accurate representation of the tree's overall size than simply adding stem diameters together. Other jurisdictions may use alternative methods, such as summing stem diameters directly or applying city-specific formulas contained within local tree protection ordinances.

Because multi-stem tree calculations can affect permit requirements, tree valuations, and significant tree determinations, property owners should always verify which methodology is required by the jurisdiction governing their project. When in doubt, consult a qualified ISA Certified Arborist or the local permitting authority.

Seattle Quadratic Diameter Method Example

Seattle-area arborists commonly use the quadratic diameter method when measuring multi-stem trees. Rather than simply adding trunk diameters together, this method combines the stems in a way that more accurately reflects the tree's overall size.

Why not just add them?

Adding the stems together would produce a diameter of 30 inches, which significantly overstates the size of the tree. The quadratic method accounts for the cross-sectional area of each stem and provides a more representative combined diameter.

Why Not Simply Add the Stems Together?

Adding the stems together would produce a diameter of 30 inches, which significantly overstates the size of the tree. The quadratic method accounts for the cross-sectional area of each stem and produces a more representative combined diameter. Because multi-stem calculations can affect permit requirements and significant tree determinations, property owners should always verify which methodology is required by their local jurisdiction.

Tree Diameter Permit Thresholds by City

Many cities and counties in the Puget Sound region regulate tree removal, major pruning, and development activities based on a tree's Diameter at Breast Height (DBH). These regulations often establish minimum diameter thresholds that determine whether a tree is considered significant, exceptional, protected, or subject to permit requirements. Because these thresholds vary by jurisdiction and are periodically updated, property owners should always verify current regulations before planning tree work.

Our arborists regularly assist property owners with tree measurements, permit applications, arborist reports, tree retention plans, and development projects throughout the Seattle metropolitan area. If your project involves a large or protected tree, we recommend reviewing the applicable municipal code or consulting an ISA Certified Arborist before proceeding.

Common Cities We Serve

• Seattle Tree Permits
• Bellevue Tree Regulations
• Tacoma Tree Permits
• Renton Tree Removal Permits
• Federal Way Tree Regulations
• Burien Tree Regulations
• Kent Tree Permits
• Issaquah Tree Protection Rules
• Mercer Island Tree Regulations
• Shoreline Tree Permits