Treescience

At Treescience, we advise government, commercial and private clients, offering an extensive range of services in the field of arboriculture, urban forestry, soil science, project arborist supervision, tree surgery, assessments and reporting, GIS tree inventories, plant health care, and expert witness reports.

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Free industry professional calculator created by Treescience

AS4970-2025:Smart Tree Protection Zone Calculator

Calculate the NRZ and SRZ radius, model multiple overlapping encroachments, and calculate the compensatory TPZ offset. Download the results as a PDF and Excel spreadsheet.

Open the AS4970 Smart Calculator
Worked example from the calculator. A 600 mm stem gives a Notional Root Zone radius of 7.20 metres (diameter × 12) and a Structural Root Zone radius of 2.67 metres. Two overlapping encroachments remove 33.47 square metres, 20.5 per cent of the zone, with the shared overlap counted only once. The calculator then solves for a compensatory radius of 8.489 metres, at which the unencroached area is back to the original 162.86 square metres.

Disclaimer

Use of the calculator within this website is free. Whilst every effort has been made to ensure the accuracy of the calculator published within this website, you choose to use it and rely on any results at your own risk. We will not under any circumstances accept responsibility or liability for any losses that may arise from a decision that you may make as a result of using the calculator.