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What you’ll learn in this lesson:
  • Define mass balance and explain why it matters for carbon projects
  • Identify regulatory and verification requirements for mass balance
  • Understand that mass balance applies to both physical stock and CO2e quantities
  • Connect mass balance to the ledger-based tracking you’ll build in this module
Mass balance is the accounting principle that the total mass of a conserved substance entering a system must equal the total mass leaving the system, plus any change in storage within the system. In carbon and fuels projects, the “substance” we track is usually a carbon-rich physical product, feedstock, or fuel—and the “system” is your project boundary. In practice, this means: every tonne of feedstock carbon you record as received should be accounted for—whether it becomes product (e.g., biochar, fuel), process loss, or inventory. Nothing should appear without traceable calculations and chain of custody. Mass balance is not just a technical check; it is the backbone of transparency and credibility in the carbon markets. It answers the question: Can we demonstrate that the attributes we claim are backed by real, traceable flows?

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Why mass balance matters

Mass balance matters for MRV and compliance because:
  • Methodologies require it. Most standards bodies (e.g., Isometric, Puro.earth, CARB, RED II) explicitly require mass balance accounting or chain-of-custody tracking for feedstocks, intermediates, and outputs.
  • Verifiers look for it. Auditors will trace reported tonnes from source events (e.g., delivery tickets, production logs) through processing and into batches or credits. Gaps or unexplained imbalances are red flags. The reported outputs (such as upgraded fuel or high-concentration CO2 injected) cannot be larger in mass than the intermediates (e.g. CO2 transported or mid-quality biogas generated).
  • Project Developers want to optimize it. Project developers are interested in optimizing the conversion of material balances at various project stages to generate the largest amount of carbon-positive product or credits. Mangrove offers an opportunity for them to analyze the efficiency at each stage.
Without a clear mass balance, a project cannot reliably defend their reported outcomes and pass verification.

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Regulatory and verification requirements

Regulators and standards bodies treat mass balance as a core safeguard against over-claiming and double-counting. Here’s how it shows up across major frameworks: The common thread: every framework requires that you can trace reported outputs back to measured inputs, with no unexplained gaps. Mangrove’s ledger system (which you’ll build in this module) is designed to satisfy these requirements.

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Physical stock vs. CO2e tracking

Mass balance can apply to different units depending on what your project tracks:
Track the physical material moving through your project:
  • Sacks of biochar (tonnes)
  • Gallons of fuel (gallons or liters)
  • Cubic meters of gas (Mcf or MMBtu)
Physical stock mass balance ensures that the amount of material you report producing or delivering is consistent with what you received and processed.
Many projects track both — physical stock through production stages and CO2e for final credit issuance. In Mangrove, each ledger can track a different unit, so you can maintain both balances simultaneously.

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Check your understanding

The total mass of a conserved substance entering a system must equal the total mass leaving, plus any change in storage within the system. Every tonne of feedstock carbon recorded should be accounted for — whether it becomes product, process loss, or inventory.
Auditors trace reported tonnes from source events (delivery tickets, production logs) through processing and into batches or credits. Gaps or unexplained imbalances are red flags — outputs cannot be larger in mass than the inputs and intermediates that produced them.
Yes. Mass balance can apply to physical stock (e.g., sacks of biochar, gallons of fuel) and to CO2e quantities (tCO2e). Many projects track both simultaneously — physical stock through production stages and CO2e for credit issuance. In Mangrove, each ledger can use a different unit.
Next, learn how to design your ledger structure in Lesson 4.2: Designing the Ledger Structure.