Tree Rooting Volume Calculator

This tree rooting volume calculator estimates the minimum rooting volume required for urban trees using evidence‑based methods from research and practice guidance. Switch between methods to match your design stage, available data (DBH, canopy, or rule‑of‑thumb), and precision requirements.

Compare the recommended rooting volume with actual available soil to identify where you need to increase provision, adjust planting density, or change species selection.

How to use this calculator

• Select a calculation method from the dropdown.
• Enter the required inputs (canopy diameter and rooting depth, or DBH and volume per cm).
• Review the recommended minimum rooting volume and explanation.

These are minimum estimates for design purposes. Site‑specific conditions (soil structure, compaction, climate, irrigation, species, conflicts with services) may require higher volumes. Seek professional arboricultural advice for critical projects.

Rooting volume calculation methods

1. Canopy-based soil volume requirement

This method calculates the total soil volume required based on the tree’s target canopy size and a recommended soil volume per square metre of canopy (typically 0.5–0.8 m³/m²). The required volume is independent of the available rooting depth — a larger canopy always needs more total soil.

• You enter: projected or target canopy diameter (m) and soil volume rate per m² of canopy (default 0.6 m³/m²).
• The calculator derives canopy area using the formula \(A = \pi r^{2}\) and multiplies by the volume rate to determine total required rooting volume.
• Optionally, you can enter the available rooting depth (m). If provided, the calculator will show how much soil surface area you need to achieve the required volume at that depth.
• If the depth is shallow (< 0.8 m) or the required area is very large, the calculator will display a warning with recommendations.

Use this method when you know the design canopy size and need to determine either (a) the total soil volume the tree requires, or (b) how much trench length or pit area is needed given a constrained rooting depth.

Guidance such as the Leeds City Council Urban Tree Planting Guidance (PDF) and the Guidelines on Soil Volume for Urban Trees (PDF) provide canopy-based soil volume recommendations for urban sites.

2. Volume per m² of canopy

Uses a volume per square metre of canopy ratio (e.g., 0.5–0.8 m³/m²), adjusted for climate, soil quality, and target lifespan.

• You enter: canopy diameter (m) and soil volume rate (m³ per m² canopy).
• Calculator computes canopy area and multiplies by your chosen rate.
• Use to test different soil provision scenarios or align with policy targets.

See MacRae’s evaluation of soil volume requirements and Which Plant Where soil volume calculation .

3. Volume per cm DBH

A volume per centimetre of DBH rule (e.g., 0.3–0.6 m³/cm) simplifies early‑stage calculations where canopy data is missing.

• You enter: target or existing DBH (cm) and volume rate (m³ per cm DBH).
• Calculator multiplies to estimate minimum rooting volume.
• Use when you have DBH survey data or need simple rules for non‑specialist teams.

See MacRae’s soil volume evaluation and Guidelines on Soil Volume for Urban Trees .

4. Fixed volume per tree (benchmark approach)

Uses a fixed minimum rooting volume per tree (e.g., 12 m³, 20 m³, or 30 m³) based on practice recommendations and local standards. Useful for early feasibility stages.

• You enter: a target fixed volume per tree.
• Calculator reports this as minimum recommended volume for comparison with actual trench or pit volume.
• Use when briefing architects or setting specification minimums.

See Lindsey & Bassuk’s “Redesigning the urban forest from the ground below” , DeepRoot’s recommended soil volumes , and Bruse Group’s overview .

Connected vs. isolated rooting volumes

The calculations above assume isolated trees in individual pits. Trees in connected soil volumes (continuous trenches, soil beds, or structural soil systems) can achieve healthy growth with approximately 20% less volume per tree due to improved root access and spatial efficiency.

Example: A continuous trench 2 m wide × 1 m deep × 15 m long (30 m³ total) serving four street trees provides 7.5 m³ per tree. With connectivity benefits, this can perform comparably to isolated pits of 9–10 m³ per tree.

Why connected volumes work better:

• Roots exploit the entire shared volume rather than being confined by pit walls
• Better moisture and nutrient distribution across the system
• Improved structural anchorage through unrestricted lateral root growth
• Reduced compaction and edge effects

Design recommendation: Where feasible, prioritize connected trenches or structural soil over isolated pits. The primary benefit is improved tree performance and reliability, with modest volume reduction as a secondary advantage.

Key research: Lindsey & Bassuk on connected soil volumes and DeepRoot’s guidance on continuous trenches .

The table below provides a quick guide to selecting the most suitable approach.

Situation	Recommended method	Notes
Known target canopy spread from design	Canopy-based soil volume requirement	Calculates total required volume based on canopy area × rate. Optionally shows required surface area if depth is provided.
Testing different soil provision scenarios per m² canopy	Volume per m² canopy	Adjust the volume rate to test scenarios or align with policy targets.
Existing trees with DBH survey data only	Volume per cm DBH	Assess whether current soil provision constrains growth.
Early concept design, limited tree data	Fixed volume per tree	Set a conservative minimum (20–30 m³) based on municipal standards.

By providing multiple calculation methods linked to published research and practice guidance, this tool is designed to be transparent, defensible, and adaptable to different project contexts.