Enter one trunk measurement and get the protection zone radius, the structural root zone and how far your slab, driveway or pool can go before an arborist has to justify it. Built to the AS 4970 method, including the 2025 revision.
1 · Measure the trunk
2 · Your proposed works (optional)
Result
This is an indicative calculation using the published AS 4970 method, not a substitute for an arboricultural assessment. Councils and your project arborist assess encroachment on the actual root plate, which can be lopsided, and can require root mapping. Figures are rounded to the nearest 0.1m.
The method comes from AS 4970, Protection of trees on development sites. It is one line of arithmetic: the protection zone radius is twelve times the trunk diameter measured 1.4 metres above the ground. A 400mm trunk gives a 4.8 metre radius, measured out from the centre of the trunk in every direction.
Two limits sit on top of that. The standard sets a minimum radius of 2 metres and a maximum of 15 metres, so a very small tree still gets a working setback and a very large one does not consume the whole block. The maximum can be exceeded where the crown itself needs protecting.
There is a catch that trips people up constantly. Councils write their thresholds in circumference. The standard works in diameter. A tree at Kingston’s 110cm circumference trigger is a 35cm diameter trunk, which is a 4.2 metre protection zone. Measuring the wrong one out by a factor of pi is the single most common mistake we see on early site plans, which is why the calculator above takes either.
The protection zone is about keeping the tree healthy. The structural root zone is a much smaller circle close to the trunk holding the roots that keep the tree standing up. Its radius comes from a separate formula using the trunk diameter measured immediately above the root buttress, and for trunks under 150mm the standard simply sets it at 1.5 metres.
The distinction matters commercially. A modest encroachment into the outer protection zone is usually a conversation. Any encroachment into the structural root zone is a stability question, and it is where a design gets sent back.
As a working guide, up to around 10 per cent of the zone area is treated as minor and generally proceeds with standard protection measures — fencing, ground protection, no storage or washout inside the zone. Between roughly 10 and 20 per cent is moderate, and needs a project arborist to demonstrate the tree will tolerate it. Beyond that you are into root mapping, non-destructive excavation and tree-sensitive design rather than a percentage you can argue on paper.
The 2025 revision of AS 4970 made room for more of this than the 2009 version did, provided the investigation work backs it up. It also introduced a root-zone term, the NRZ, sitting alongside the TPZ, replaced DBH with DSH (diameter at standard height — still measured at 1.4 metres), and split the old tree management plan into a protection plan and a written specification. If you are comparing an older arborist report against a new one, the labels changed but the twelve-times multiplier did not.
This is the part no calculator can answer, because every council writes its own rule. Some run a local law with a hard size trigger. Some rely entirely on planning overlays. The thresholds are written at different heights on the trunk, which means the same tree can be protected in one municipality and exempt in the next street over.
Below is where six councils across south east Melbourne and the Mornington Peninsula currently sit — the areas we build in. Checked September 2026, direct from each council. Fees are set by council and by state regulation and are indexed, so confirm the current figure before you budget it.
| Council | What controls it | Size that triggers a permit | Permit fee | Significant tree register |
|---|---|---|---|---|
| Bayside | Local Law, plus a planning permit where a Heritage, Significant Landscape or Vegetation Protection Overlay applies | Trunk circumference over 155cm at 1m above ground. Multi-trunk trees add the four largest trunks together | Administration fee — amount not published online | Yes |
| Kingston | Community Local Law No. 5 and the planning scheme — in most cases one or the other applies | Local law: base circumference over 110cm, or any multi-stemmed tree. Planning: over 5m tall and 4m canopy and over 0.5m circumference at 1.4m | $130 per tree, waived for pensioner concession and DVA gold card holders. Planning permit $233.10 | Yes — published as a PDF |
| Glen Eira | Canopy Tree Protection Local Law and planning scheme Clause 52.37. Where both bite, the planning scheme prevails | Local law: a palm over 8m, a stump circumference of 140cm at ground level, or a tree over 5m with 140cm circumference at 1.4m | Local law permit is free | Yes — Classified Tree Register, publicly searchable |
| Frankston | Tree Protection Local Law 2016 No. 22, plus planning permits under overlays such as the Significant Landscape Overlay | Trunk circumference of 110cm or more at the base. Also triggered by works affecting more than 10% of the tree protection zone, or pruning over a third of the crown — including cumulatively | Application fee applies — amount not published in the local law | None found |
| Mornington Peninsula | Planning overlays only — no separate tree local law. Controls vary block by block | No fixed size trigger. Whether a permit is needed depends on the overlays on your title, checked through the Shire’s property tool | Planning permit fees apply | None found |
| Casey | Casey Planning Scheme — triggered by an Environmental Significance, Vegetation Protection, Significant Landscape or Heritage Overlay | Over 5m tall, canopy at least 4m, or trunk circumference over 0.5m at 1.4m. Native vegetation rules also apply above 4,000 sqm | Planning permit fees apply | Yes — within the Significant Tree Strategy |
Where a fee or register is shown as not published, it was not available on the council’s own site at the time of checking — call them rather than assume there isn’t one.
Since 15 September 2025, planning scheme Clause 52.37 has protected canopy trees across every Victorian planning scheme. A canopy tree is one meeting all three tests: over 5 metres tall, trunk circumference over 0.5 metres at 1.4 metres, and a canopy at least 4 metres across. A permit is needed to remove one anywhere on a vacant lot, and on a developed lot within 6 metres of the street frontage or 4.5 metres of the rear boundary. It applies in the General, Neighbourhood and Growth residential zones, Mixed Use, Township, and Housing Choice and Transport — but not in Low Density Residential.
That clause is the reason tree questions became a live issue on knockdown rebuilds in the last year. Plenty of blocks that would have been cleared without a second thought in 2024 now need a permit for the tree near the front fence. We wrote up how that plays out on a real site in tree protection zones, canopy trees and overlays, including what it cost us to keep a tree on our Moorabbin build.
Rarely on its own. It sets where you can and cannot disturb the ground without justification. Most designs absorb it by moving a footing, changing a footing type, using a suspended slab over the zone, or relocating a driveway. What it does do is change the answer before you draw — which is why it is worth checking at feasibility rather than after a design you like has been drawn around a tree you cannot keep.
The zone does not stop at the fence. If a neighbouring tree’s protection zone reaches into your block, your works are inside it and the same assessment applies. You have no right to damage the roots, and you generally cannot remove or prune the tree without the owner’s consent and, where a permit is triggered, council approval.
No. Councils that require an arborist report require one from a qualified arborist, usually at AQF Level 5, working to the council’s own reporting guidelines. This tool gives you the same arithmetic they start from, so you can see roughly where you stand before you commission anything.
Correct, and the standard acknowledges it. The circle is a starting assumption. Where a design pushes into the zone meaningfully, the next step is root investigation — typically non-destructive excavation to find where the roots actually run. Sometimes that opens a design up rather than closing it down.
No, and it is an expensive idea. Removing a protected tree without a permit exposes you to penalties under the local law or the planning scheme, and councils routinely require replacement planting on top. It also tends to colour every subsequent dealing you have with that council on that site.
If you have a tree you want to keep — or one you suspect is going to be a problem — send us the numbers. Tim will come back to you with a straight read on whether it changes your design, and what it typically costs to work around. No charge, no obligation.
Your calculator figures are sent with the enquiry so Tim has the context. Want the overlays on your block checked too? Run the free knockdown rebuild feasibility check — it reads your address against Victoria’s official planning data, including vegetation and significant landscape overlays.