# Soil Carbon Stock Calculator

> Estimate the organic carbon stored in a soil layer from carbon %, bulk density, depth and stone content, in tonnes C and CO₂e per hectare and field.

Category: Agriculture · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/soil-carbon-stock-estimate-calculator

Soil carbon stock is the mass of fine soil in the layer times its organic carbon content. Multiply by 44/12 to express it as CO₂.

Also called: SOC stock calculator, Soil organic carbon stock calculator.

## Inputs
- Soil organic carbon (unit %; default 1.2)
- Bulk density (unit g/cm³; default 1.35)
- Layer depth (unit cm; default 30)
- Stones and gravel (optional) (unit % by volume; default 5; optional)
- Area (default 10)
- Area in (options: Hectares, Acres; default ha)

## Results
- Carbon stock
- As CO₂ equivalent
- Carbon stock per acre
- Carbon in the area
- CO₂ equivalent in the area
- Fine soil in the layer

## Formula

```
SOC stock (t C/ha) = SOC % × Bulk density (g/cm³) × Depth (cm) × (1 − Coarse fraction);  CO₂e = C × 44 ÷ 12
```

Where:
- SOC %: organic carbon by mass of fine soil
- Bulk density: dry mass per volume of soil
- Coarse fraction: stones and gravel share of the volume
- 44/12: mass ratio of CO₂ to C

## Worked example
1. Stock = 1.2 × 1.35 × 30 × 0.95 = 46.17 t C/ha.
2. CO₂e = 46.17 × 44 ÷ 12 = 169.29 t/ha; over 10 ha, 461.7 t C.

**Result:** The top 30 cm holds about 46 t of organic carbon per hectare, equivalent to 169 t of CO₂.

## What the result means

To compare stocks over time or between practices, sample to the same depth, or better, compare equal soil masses, because tillage and compaction change bulk density.

## Assumptions and limits
- SOC and bulk density are averages for the whole layer.
- A single estimate is not a verified carbon credit; carbon schemes set their own sampling and measurement rules.
- If you only have organic matter %, a conversion factor is needed, and it varies between soils.

## Questions

### Why multiply by 44/12?

A CO₂ molecule weighs 44 units and its carbon atom 12, so 1 t of carbon corresponds to 3.67 t of CO₂.

### Can I sum several layers?

Yes. Calculate each layer with its own carbon %, bulk density and depth and add the stocks.

## Related calculators
- [Lime Application Calculator](https://calculators.geekmidst.com/calculators/soil-lime-requirement-calculator)
- [Compost Volume Calculator](https://calculators.geekmidst.com/calculators/compost-volume-calculator)
- [Soil Water Deficit Calculator](https://calculators.geekmidst.com/calculators/soil-water-deficit-calculator)

Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/soil-carbon-stock-estimate-calculator