Soil Organic Carbon Calculator & SOC ↔ SOM · Carbon Stock
Measures soil carbon for soil health
Convert SOC ↔ SOM (Van Bemmelen 1.724) and compute your soil's carbon stock in tonnes per hectare and CO₂-equivalent from organic carbon, bulk density and depth — with a soil-health rating.
Enter your soil test
Typical topsoil bulk density 1.2–1.5 g/cm³; sandy soils higher, organic soils lower.
Next: build carbon (and fertility) with compost/FYM, residue retention, cover crops and reduced tillage — even +0.1% SOC adds roughly 1.95 t C/ha. Organic matter holds water and nutrients, so raising it pays back in yield.
Stock uses SOC × bulk density × depth. The 1.724 factor is a convention — actual SOC:SOM varies with soil.
Soil organic carbon — key facts
- SOM = SOC ×
- 1.724 (Van Bemmelen)
- Carbon stock
- SOC% × bulk density × depth(cm)
- 1 t C =
- 3.67 t CO₂e
- Low / medium SOC
- <0.5% / 0.5–0.75%
- Good / high SOC
- 0.75–1.5% / >1.5%
- Topsoil bulk density
- 1.2–1.5 g/cm³
- Build SOC with
- compost, residue, cover crops
- Privacy
- Runs in your browser; nothing uploaded
The number behind healthy soil
Soil organic carbon is the single best indicator of soil health — it drives structure, water-holding, nutrient supply and the living biology that makes a soil productive. Lab reports quote it as a percentage, sometimes as organic carbon (SOC) and sometimes as organic matter (SOM); the two are linked by the Van Bemmelen factor, SOM = SOC × 1.724. This tool converts between them and, more usefully, turns the percentage into a carbon stock — the actual tonnes of carbon per hectare — using your bulk density and sampling depth.
That stock matters two ways. Agronomically, it sets a baseline you can track: building SOC with compost, retained residues, cover crops and reduced tillage steadily improves fertility, and even +0.1% is several tonnes of carbon per hectare. Environmentally, every tonne of soil carbon represents about 3.67 tonnes of CO₂ drawn from the air, which is the foundation of soil carbon credits. Measure with a lab test, enter the figures here, and use the rating to see where your soil stands and how far it can go.
Convert SOC ↔ SOM
Switch between organic carbon and organic matter with the standard factor.
Get the carbon stock
Turn a percentage into tonnes of carbon per hectare and CO₂-equivalent.
Rate soil health
See whether your SOC is low, medium, good or high for cropping.
Track improvement
Re-measure over seasons to see organic-matter building pay off.
Frequently Asked Questions
How do I convert SOC to SOM?+
Multiply soil organic carbon by the Van Bemmelen factor of 1.724: SOM% = SOC% × 1.724. So 1% organic carbon is about 1.72% organic matter. To go the other way, divide SOM by 1.724. This tool does both and also computes the carbon stock.
What is soil organic carbon (SOC)?+
SOC is the carbon held in soil organic matter — decomposed plant and animal residues, microbes and humus. It's a key indicator of soil health: higher SOC means better structure, water-holding, nutrient supply and biological activity. Lab reports give it as a percentage.
How do I calculate carbon stock per hectare?+
Carbon stock (t/ha) = SOC% × bulk density (g/cm³) × depth (cm). For example, 1% SOC at 1.3 g/cm³ over the top 15 cm is about 19.5 t of carbon per hectare. Enter your soil-test SOC, bulk density and sampling depth to get the stock.
Why does bulk density matter?+
Carbon stock depends on the mass of soil, not just its carbon concentration — and that mass depends on bulk density. A compacted soil holds more mass (and carbon) per unit depth than a loose one. Typical topsoil is 1.2–1.5 g/cm³; use your measured value for accuracy.
What is a good soil organic carbon level?+
It varies by climate and soil, but as a rough topsoil guide: below 0.5% is low, 0.5–0.75% medium, 0.75–1.5% good, and above 1.5% high. Many intensively cropped tropical soils sit below 0.5%, so building SOC is a common goal.
How is soil carbon linked to CO₂?+
Soil carbon comes from CO₂ that plants fixed and returned to the soil. Each tonne of soil carbon represents about 3.67 tonnes of CO₂ (the mass ratio of CO₂ to C, 44/12). Building soil carbon therefore removes CO₂ from the air — the basis of soil carbon credits.
How can I increase soil organic carbon?+
Add organic matter (compost, FYM, green manure), keep crop residues on the field, grow cover crops, reduce tillage, and keep the soil covered and biologically active. Gains are gradual — often 0.01–0.1% SOC a year — but compound into better fertility and water-holding.
How much carbon is in 0.1% more SOC?+
About SOC-change × bulk density × depth tonnes per hectare. At 1.3 g/cm³ over 15 cm, raising SOC by 0.1% adds roughly 2 t of carbon per hectare (≈7 t CO₂e) — a meaningful climate and fertility gain over time.
Is the 1.724 factor always right?+
It's a long-standing convention assuming organic matter is 58% carbon, but the true ratio varies with soil and material (factors of 1.7–2.0 are reported). Use 1.724 for standard reporting; for precise work, use a locally calibrated factor or measure both directly.
Does this measure or estimate carbon?+
It calculates stock and conversions from values you supply (from a soil test). It doesn't measure SOC itself — that requires a laboratory analysis (e.g. Walkley-Black or dry combustion). Enter your lab SOC% (or SOM%) and the tool does the rest.