The Biodiversity Net Gain Metric Explained

Here we explain in detail the cultivation of the Biodiversity Net Gain Metric (BNG Metric), its uses and its importance within the context of the BNG policy.

What is The Biodiversity Net Gain Metric?

The biodiversity net gain (BNG) metric was introduced in the Environment Act 2021. It is a crucial calculation tool that reshapes our approach to development projects. 

Years of continuous construction and development have caused biodiversity loss to the point of mass species endangerment, habitat destruction, and risks to the livelihoods of animals, wildlife and us.

BNG ensures that development projects can continue onwards without harming the environment. Developers must now prove they can achieve on-site BNG, and if not then off-site BNG, or buy statutory credits as a last resort. The net gain of biodiversity, including the loss at the development site and the compensations over a 30 year period, must result in a 10% net gain.

Other biodiversity offsetting schemes such as habitat parcels might aim for no net loss (‘NNL’), however, BNG’s bold 10% gain has received concerns that it might be hard to achieve and manage over the long term period.

The BNG metric, amongst other statutory measures and detailed guidance, challenges these claims by bringing a clear, measured framework to regulate the ecologists’ measurements of biodiversity and ensure a structured approach is universally delivered.

The metric calculates the biodiversity of a site pre-development, what it will be post-development, and exactly how much work is required to meet the 10% gain. Using various condition assessment sheets, the standardised unit of measurement quantifies ecological value based on each natural environment; analysing habitat features and specifics in great detail.

How the Metric is Valuable for Biodiversity Net Gain

The metric is not only valuable but instrumental for biodiversity net gain (BNG), allowing developers to continue forth with their projects using the calculations afforded by the metric, in line with the appropriate habitat-based approach that protects our environment. 

It means that sites across England will be given adequate land management for 30 years, prioritising the preservation and enhancement of the natural environment. 

The metric is valuable for BNG as it enforces a calculated, structured approach. One universal metric simplifies the new legislation and alleviates concerns of how the mandatory biodiversity net gain will suddenly be achieved. 

The metric uses a habitat-based methodology to assess a site’s condition, allowing ecologists to make predictions about the change in biodiversity before and after development occurs.

The metric is valuable as it is complex and rigid in measuring biodiversity, and it also accommodates small-scale development projects through the SSM (Small Sites Metric). 

BNG is currently mandatory for major development projects, but from April 2024 will also be applicable for smaller projects. By offering 2 versions of the calculations, the metric proficiently allows biodiversity to be measured, regardless of scale.

Biodiversity Metrics Updates

The Biodiversity Metric has evolved over the years through successive updates, incorporating feedback and improving its effectiveness of administering biodiversity assessments.

Biodiversity Metric 1.0

Biodiversity Metric 1.0, the inaugural version launched in 2012, laid the foundation for subsequent developments. Piloted initially, it underwent changes based on early tests and suggestions from various industry experts.

The updates included expanding coverage to more habitat types, improving consideration for ecological connectivity and integrating with a new spreadsheet tool.

These adjustments aimed to create a more comprehensive and effective tool for measuring biodiversity, considering a diverse range of habitats within the development site.

Biodiversity Metric 2.0

By 2019, Biodiversity Metric 2.0 emerged with considerable refinements to enhance the accuracy of biodiversity measurements.

This version introduced the measurement of both area and linear habitats, covering intertidal habitats and providing more comprehensive data on river metrics.

Importantly, it addressed and rectified issues from the previous version, such as inaccuracies in measurement due to data outside the chosen plot of land, errors in dropdown tabs, and the omission of off-site habitats.

The improvements aimed to provide a more robust and reliable metric for assessing biodiversity, aligning with the evolving needs of developers and ecological experts.

Biodiversity Metric 3.0 / Biodiversity Metric 3.1

Biodiversity Metric 3.0, released in 2021, marked a significant milestone in response to extensive testing and consultations.

Key changes included incorporating a contextual understanding in habitat creation, as well as altering the target for improved biodiversity from 32+ years to 30+ years. A more concise goal is simpler to implement, and remains a long enough period to achieve significant biodiversity gain.

The subsequent release, Biodiversity Metric 3.1 in 2022, brought further improvements in accessibility, clearer definitions, and updated information on how ecologists should apply the metric correctly.

Biodiversity Metric 4.0

March 2023 saw the introduction of Biodiversity Metric 4.0, representing a substantial update with a focus on enhancing the user experience.

Natural England emphasised its user-friendly nature while introducing changes such as name revisions to habitat types, the inclusion of new habitat categories, and other adjustments based on iterative detailed feedback.

Despite expectations of an incorporation of marine net gain for English waters, the update concentrated on usability enhancements. Biodiversity Metric 4.0, labelled a ‘substantial update,’ underlines the ongoing efforts to streamline and improve the metric based on practical user experiences.

Uses for The Biodiversity Net Gain Metric

The uses of the BNG metric vary depending on who is using it. The many parties involved in the development process benefit from the comprehensive biodiversity metric.

Developers, during assessments, can utilise the metric to gauge and plan how their site will specifically achieve the 10% gain. This considers the types of habitat at their site, and the features of the nature, to determine if on-site BNG is applicable or if off-site BNG must be explored, and if so to what degree. 

Landowners can leverage the metric to assess the current biodiversity value of their land, and if they are applicable to be turned into biodiversity units for developers to purchase.

The metric is a standardised habitat based measurement, meaning that developers BNG requirements are directly in line with the land owners’ calculated BNG units, ensuring consistency that means everything works well to achieve the 10% gain.

What’s more, local planning authorities rely on the metric to verify the published biodiversity values and planned improvements, in order to choose to grant or deny planning applications to the developers.

Habitat Types

Sun shining through trees

The very first stage of BNG is a habitat assessment in order to understand the existing biodiversity of a site. Examples of this are the consideration of land and intertidal areas, where the metric has to account for hedgerows and lines, rivers, line of trees, streams or other water bodies within the boundaries of the site.

The metric considers a variety of ecosystems, from agricultural and grassland areas to habitat mosaics, heathlands and lines or trees, quarries, scrub, wetland, woodlands and more. Each habitat contributes differently to biodiversity, and some are rarer than others. Some habitats are irreplaceable, meaning they require close attention and monitoring.

Throughout the metric upgrades, they grew to encompass a vast range of habitat types, to ensure that no type is left uncovered. This is to make it run as smoothly as possible in delivery, as the complexity and diversity of nature is hard to quantify and categorise.

The first version failed to consider key factors such as ecological connectivity or habitat diversity, whereas the latest version represents a substantial metric that has responsively moulded to ecological priorities.


The Biodiversity Net Gain Metric employs dedicated calculation tools, such as the Biodiversity Metric 4.0 Calculation Tool, to process the gathered data effectively. 

The metric’s calculation includes a meticulous and systematic approach into the biodiversity value of development sites pre development and post development. They also determine a condition assessment of potential biodiversity sites, and the forecasted biodiversity value if to be bought by a developer.

The calculation analyses factors such as local nature, habitat type, condition, size and significance to attain a thorough collection and summary of data. The ecologists can input this data and the metric generates precise scores of biodiversity.

The score acts as a quantitative representation of the overall biodiversity of a site, how much is lost in development, and the specific amount of gain required to meet the 10% requirement.

This score is then key for developers to consider their route of BNG in the development project. This is impacted by other tools such as the spatial risk multiplier, which highlights that less work is required when the off-site location is close to the original development site. 

This is so that compensatory efforts are meaningful to local biodiversity, instead of simply bought in less expensive areas that are far from the original site and vary from the habitats local to the initial area. The spatial multiplier encourages the appropriate types of habitats are restored and enhanced.

Using the Metric

Leveraging the Biodiversity Net Gain (BNG) Metric involves a systematic and structured approach aimed at comprehensively assessing and enhancing biodiversity within the context of development projects.

Ecologists play a central role in employing the metric, initiating the process by conducting a thorough assessment of the current state of biodiversity on a given site. This evaluation encompasses critical factors such as habitat quality, condition, and location.

The BNG Metric, particularly in its latest iteration, Biodiversity Metric 4.0, provides an accessible and user-friendly interface, streamlining the data collection and assessment process.

The metric becomes a collaborative tool, bringing together ecologists and developers to ensure a shared understanding of the development plans and their potential impact on biodiversity.

By engaging in a comprehensive dialogue, stakeholders can anticipate and plan for the post-development biodiversity state. Through the comparison of pre and post-development measurements facilitated by the metric, ecologists can precisely identify the biodiversity deficit and strategize interventions to achieve a net gain of at least 10%.

Versions like Biodiversity Metric 4.0 contribute to this collaborative effort by offering calculation tools and user guides that enhance the consistency and standardisation of the application.

The metric, through its user-friendly features, enables ecologists and developers to navigate the intricacies of biodiversity assessments efficiently.

By incorporating the metric into the planning process, stakeholders can align their objectives with the broader environmental goals, ensuring that development projects not only meet regulatory requirements but also contribute positively to the enhancement and preservation of biodiversity.

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