What does the biochar carbon calculator do?

The Carbon Workbench biochar calculator estimates the net carbon dioxide equivalent (tCO₂e) sequestered per tonne of biomass processed into biochar. It models the complete chain from raw feedstock through to verified carbon credits, accounting for all the key variables that affect the final credit yield.

Unlike simple spreadsheet estimates, the calculator shows you each step of the calculation - so you can see exactly why a change in moisture content or yield ratio changes the output. This transparency is particularly useful when preparing figures for a Gold Standard or Puro.earth submission, where auditors will scrutinise every assumption.

Key inputs

Biomass input - total wet feedstock entering the plant, before drying or moisture removal
Moisture content - the percentage of that wet feedstock that is water; this is what converts wet biomass into dry biomass
Biochar yield - the proportion of dry biomass that becomes finished biochar during pyrolysis (typically 20-35%)
Carbon content - the percentage of the finished biochar mass that is elemental carbon (typically 60-80%)
Process emissions - the deduction applied to gross CO₂e for plant energy use, startup fuel and other process losses
Permanence discount - the deduction applied after emissions losses to reflect durability or BC+100-style stability evidence
Logistics / application emissions - an optional extra deduction for transport, handling or spreading emissions outside the plant boundary
Creditable share - the proportion of the screened net removal that you expect to be issuable after methodology rules and exclusions

How is biochar carbon calculated?

The biochar carbon calculation follows this chain:

Dry mass = Wet biomass × (1 − moisture fraction)
Biochar produced = Dry mass × yield fraction
Carbon in biochar = Biochar × carbon fraction
Gross CO₂e = Carbon × 3.667 (molecular weight ratio of CO₂ to C)
Net CO₂e = Gross CO₂e − process emissions − logistics / application losses − permanence discount − any crediting haircut

The 3.667 conversion factor is the IPCC default ratio of the molecular weight of CO₂ (44) to carbon (12). The permanence discount is derived from the H/Corg (hydrogen to organic carbon) ratio, which is the internationally accepted method for assessing long-term carbon stability in biochar.

For a fuller explanation of the permanence discount, see our biochar permanence guide. If you are weighing different registry routes, the biochar methodology guide explains how Puro-style and Verra-style approaches differ in practice.

Biochar credit yields by feedstock

Feedstock type	Typical yield	Typical carbon content	tCO₂e per tonne feedstock
Woody biomass (hardwood)	28–32%	72–80%	0.45–0.65
Agricultural residues (straw)	22–28%	60–70%	0.30–0.50
Green waste / garden waste	20–25%	55–65%	0.25–0.40
Sewage sludge (dried)	30–40%	25–45%	0.15–0.30
Miscanthus / energy crops	25–30%	70–78%	0.40–0.58

These are indicative ranges only. Actual values depend on pyrolysis temperature, residence time, feedstock preparation and the specific pyrolysis technology used. Always use laboratory-measured values from the actual biochar batch for formal submissions.

Which certification standard should I use?

Three main standards certify biochar carbon credits in the voluntary carbon market:

Puro.earth Biochar Method v2 - purpose-built for biochar CDR. Highest credit prices (£60–120/t). Requires H/Corg ratio testing and permanent storage verification. Best for large-scale operations targeting premium buyers.
Verra VM0044 - part of the Verified Carbon Standard. Broader buyer base with lower prices (£15–40/t). CCP-approved by ICVCM. Good for high-volume operations where liquidity matters more than per-credit price.
Gold Standard Biochar Module - available but less commonly used in the voluntary market. Emphasises SDG co-benefits. Limited buyer liquidity compared to Puro.earth or Verra.

Use the free Methodology Selector in The Carbon Workbench to get a personalised recommendation based on your project scale, feedstock and target buyers.

For a fuller explanation of how methodology choice changes buyer fit, permanence evidence and price expectations, see which biochar methodology route fits best?

Permanence and the H/Corg ratio

The permanence of biochar carbon - how long it stays locked in soil - is assessed using the hydrogen to organic carbon (H/Corg) ratio, measured in the laboratory. A lower H/Corg ratio indicates greater permanence: