Once you have taken your measurements (DBH and above-root-flare), please insert the figures (in metres) in the appropriate spaces below. The calculator will give you both the TPZ radius and area, as well as the SRZ radius.
If you have a single stem tree, simply add the DBH in metres (e.g. 350mm = .350) to the Total DBH box below.
Alternatively, trees with up to 4 stems can be calculated by measuring DBH of each individual stem, and inserting those figures individually in the four boxes above the Total DBH box. The Total will be calculated automatically as you add each figure.