Hello, and thanks for the question.
Circumference = Pi × diameter, or Diameter = Circumference / Pi (approx. 3.14159)For a trunk circumference of 2.65 metres, the diameter would be approx. 0.84352m = 843.52mm
For an individual open‐grown Beech tree in satisfactory condition of 843.52mm trunk diameter, the basic calculation of RPA is as follows:12 x 843.52mm = 10122.24mm = 10.12m radius of RPV
For the area in square metres, the calculation would be:10.12m^2 * 3.14159 = 321.74 sq. metres
Hope this helps!