Dbh Calculator

Diameter at Breast Height (DBH) Calculator

Imperial (Inches / Feet) Metric (Centimeters / Meters)

Calculation Results

Tree DBH: 0 inches

Basal Area: 0 sq ft

*Basal area represents the cross-sectional area of the tree trunk at breast height.

function calculateDBH() { var circumference = parseFloat(document.getElementById("circumference").value); var unitType = document.getElementById("unitType").value; var resultDiv = document.getElementById("dbh-result"); var resDiameter = document.getElementById("resDiameter"); var resBasalArea = document.getElementById("resBasalArea"); var unitLabels = document.getElementsByClassName("unitLabel"); var areaLabels = document.getElementsByClassName("areaLabel"); if (isNaN(circumference) || circumference <= 0) { alert("Please enter a valid circumference measurement."); return; } // DBH = Circumference / Pi var dbh = circumference / Math.PI; var basalArea = 0; if (unitType === "imperial") { // Basal Area (sq ft) = 0.005454 * DBH^2 (where DBH is in inches) basalArea = 0.005454 * Math.pow(dbh, 2); for(var i=0; i<unitLabels.length; i++) unitLabels[i].innerText = "inches"; for(var j=0; j<areaLabels.length; j++) areaLabels[j].innerText = "sq ft"; } else { // Basal Area (sq m) = 0.00007854 * DBH^2 (where DBH is in cm) basalArea = 0.00007854 * Math.pow(dbh, 2); for(var i=0; i<unitLabels.length; i++) unitLabels[i].innerText = "cm"; for(var j=0; j<areaLabels.length; j++) areaLabels[j].innerText = "sq m"; } resDiameter.innerText = dbh.toFixed(2); resBasalArea.innerText = basalArea.toFixed(4); resultDiv.style.display = "block"; }

Understanding Diameter at Breast Height (DBH)

Diameter at Breast Height (DBH) is the standard method used by foresters, arborists, and ecologists to measure the size of a standing tree. It provides a consistent baseline for calculating tree volume, age, biomass, and overall forest health.

How to Measure DBH Correctly

The standard "breast height" is defined globally as 4.5 feet (1.37 meters) above the forest floor on the uphill side of the tree. To calculate DBH manually using this tool:

1. Wrap a measuring tape around the tree trunk at exactly 4.5 feet above the ground.
2. Ensure the tape is level and not slanted.
3. Record the circumference (the distance around the trunk).
4. Input that number into the calculator above to find the diameter.

The Mathematical Formula

Since tree trunks are roughly cylindrical, we use the formula for the diameter of a circle:

Diameter = Circumference / π (3.14159)

What is Basal Area?

The calculator also provides the Basal Area. This is the cross-sectional area of the tree trunk at breast height. In forestry management, basal area is used to determine "stocking levels"—essentially how crowded a forest is. It helps land managers decide if a forest needs thinning to promote the growth of remaining trees.

Practical Example

If you measure an Oak tree and find that the circumference at 4.5 feet is 31.4 inches, the calculation would be:

• DBH: 31.4 / 3.14159 = 10.00 inches
• Basal Area: 0.005454 × 10² = 0.5454 sq ft

Common Measurement Challenges

• Sloping Ground: Always measure from the uphill side of the tree.
• Leaning Trees: Measure 4.5 feet along the underside of the lean, following the angle of the trunk.
• Forked Trees: If the tree forks below 4.5 feet, it is usually recorded as two separate trees. If it forks above 4.5 feet, it is recorded as one tree.
• Large Swellings: If there is a large burl or branch swell at 4.5 feet, measure just above the swelling where the trunk returns to a normal shape.