Measuring timber diameter is typically done using a specialized tool that simplifies the process, converting circumference measurements directly into diameter readings.
The Standard Method
Normally, timber diameter is measured with a special tape marked in cm diameter, known as a girthing tape, which is placed round the circumference of the tree or log.
This method is widely used because it provides a quick and efficient way to obtain the diameter without needing to perform calculations.
Understanding the Girthing Tape
- Special Marking: Unlike a standard measuring tape marked in length (cm or inches), a girthing tape is specifically calibrated to display diameter readings based on the circumference measurement. It uses the mathematical relationship between circumference and diameter (Circumference = π * Diameter).
- Diameter Classes: Some girthing tapes are marked in rounded down 1 cm diameter classes for easier reading and data recording.
- Zero Point: The zero point on all these tapes is the outside edge of the D ring. This ensures consistent measurements when wrapping the tape around the timber.
Steps for Measuring Diameter
Using a girthing tape is straightforward:
- Obtain a girthing tape.
- Locate the zero point, which is typically at the outside edge of the D ring.
- Place the tape round the circumference of the tree or log at the point where the diameter is to be measured (standard heights or specific points for logs).
- Pull the tape snug against the timber surface.
- Read the diameter measurement directly from the tape where the zero point aligns with the tape scale.
| Tool Used | Measurement Principle | Reading Obtained Directly |
|---|---|---|
| Girthing Tape | Measures circumference; scale is calibrated to show diameter. | Diameter |
This specialized tape eliminates the need to measure the circumference and then divide by Pi (π) to find the diameter, making fieldwork much more efficient.
