Calculator
Tree zone calculator
Work out the tree protection zones under AS 4970:2025, then measure real encroachment against your site plan.
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What it does
Enter a tree's diameter and the calculator returns its Notional Root Zone, Tree Protection Zone and Structural Root Zone to AS 4970:2025. Trace your site plan over the zones to measure how much of the root zone a proposed structure takes, and whether the result is a Minor, Moderate or Major Encroachment.
- NRZ, TPZ and SRZ from the diameter at standard height
- Encroachment measured as a percentage of the root zone
- A scaled plan you can print or export to PDF
The tool runs the standard's calculations. It does not reproduce any AS 4970:2025 text, tables or figures, and the project arborist still sets the on-ground Tree Protection Zone.