You must know the diameter or the radius.
https://m.wikihow.com/Calculate-the-Circumference-of-a-Circle
https://m.wikihow.com/Calculate-the-Circumference-of-a-Circle
Without one of those measurements, you're stuck.
1. Measure the Diameter: Select a point on the trunk that you want to measure. This point should be at breast height, which is typically around 1.4 meters (4.5 feet) above the ground.
- Wrap a measuring tape around the trunk at this point, making sure it is parallel to the ground. If the tree is large, you may need a measuring tape of sufficient length or a string that you can later measure.
- Read and record the measurement. This is the diameter of the tree.
2. Calculate the Circumference: Once you have the diameter, you can determine the circumference by using a simple mathematical formula.
- Use the formula: Circumference = π × Diameter
- Alternatively, you can also use the formula to calculate the circumference by multiplying the diameter by 3.14, which is an approximation of the mathematical constant π (pi).
Remember that this method will give you an estimation of the tree's circumference, but it may not be entirely accurate due to irregularities in the trunk. For a more precise measurement, it is recommended to use more advanced tools, such as a clinometer or laser rangefinder, which are typically used by arborists and foresters.