Soil Carbon Calculator

Enter your land area, soil organic matter percentage, soil bulk density, and land management practice to estimate how much carbon is stored in your soil. You'll get back the total soil organic carbon (SOC) stock in tonnes per hectare, along with a CO₂ equivalent figure and a breakdown comparing your practice against baseline conventional tillage.

ha

Total area of land you want to assess in hectares.

cm

Depth to which soil carbon is being measured. Standard is 0–30 cm.

g/cm³

Typical values: sandy soils ~1.5, loamy soils ~1.3, clay soils ~1.1.

%

Measured SOM % from a soil test. SOC is approximately 58% of SOM.

%

Percentage of soil volume occupied by rock fragments (>2 mm). Enter 0 if negligible.

Select the management approach applied to this land parcel.

years

How long this practice has been in place. Affects cumulative sequestration estimates.

tC/ha/yr

If you have a site-specific measured rate, enter it here. Otherwise leave 0 to use the practice-based estimate.

Results

Total SOC Stock

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SOC Stock per Hectare

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CO₂ Equivalent (Total)

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Estimated Cumulative Sequestration vs Baseline

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Annual Sequestration (Total Farm)

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Practice Carbon Factor vs Baseline

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Carbon Stock Breakdown

Results Table

Frequently Asked Questions

How is soil organic carbon (SOC) calculated from soil organic matter (SOM)?

Soil organic carbon is approximately 58% of soil organic matter, based on the van Bemmelen factor. So if your soil test shows 3.5% SOM, your SOC is roughly 2.03%. This calculator uses that conversion automatically when you enter your SOM percentage.

What is soil bulk density and why does it matter?

Bulk density is the mass of dry soil per unit volume (g/cm³), including pore spaces. It's essential for converting a percentage figure (like SOC%) into an actual mass of carbon stored per hectare. Compacted or sandy soils tend to have higher bulk density (~1.5 g/cm³), while organic-rich or clay soils are lower (~1.0–1.1 g/cm³).

Which land management practice sequesters the most carbon?

Practices that minimise soil disturbance and add organic matter consistently outperform conventional tillage. Agroforestry and silvopasture systems typically rank highest, followed by permanent pasture, no-till with cover crops, and biochar amendment. Even switching from conventional to no-till can sequester an additional 0.3–0.5 tC/ha/year.

What does the CO₂ equivalent figure mean?

Carbon dioxide equivalent (CO₂e) converts the mass of carbon into the equivalent mass of CO₂ using a factor of 3.67 (the molecular weight ratio of CO₂ to C). This makes it easier to compare soil carbon values with broader greenhouse gas inventories or carbon market standards.

How do I apply biochar to a field, and how much carbon does it add?

Biochar is typically applied at rates of 1–20 tonnes/ha and incorporated into the topsoil by light tillage or surface spreading before rainfall. It is highly recalcitrant and can persist in soil for hundreds to thousands of years. This calculator applies a modest additional sequestration factor for biochar amendment compared to standard no-till.

What sampling depth should I use?

The standard reference depth for soil carbon reporting is 0–30 cm, which is used by most national inventories and carbon credit standards including the Verra Verified Carbon Standard. However, deeper sampling (to 100 cm) may be required for some agroforestry or permanent pasture verifications.

Can I use this calculator for carbon credit verification?

This tool provides estimates based on widely used scientific relationships and practice-based sequestration rates. For formal carbon credit issuance under verified standards (VCS, Gold Standard, BCarbon), you will need accredited soil sampling, laboratory analysis, and third-party verification. Use these results for planning and farm management decisions.

Why does rock fragment content affect the result?

Coarse rock fragments (particles >2 mm) occupy volume in the soil profile but contain negligible organic carbon. Correcting for rock fragment content ensures you don't overestimate the carbon-bearing fine earth fraction, which is important for accurate SOC stock calculations in stony or skeletal soils.

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