Material assumptions (typical values)
Topsoil composition varies widely. The following assumptions are used to produce an indicative typical value:
Assumed organic matter (SOM) content: 3% by mass
Conversion of SOM to organic carbon (SOC): carbon ≈ 58% of SOM (Van Bemmelen factor)
Carbon to CO₂ conversion factor: 3.67
Carbon storage calculation (per tonne of topsoil)
Step 1 – Organic matter per tonne:
1,000 kg × 3% = 30 kg SOM
Step 2 – Convert SOM to soil organic carbon:
30 kg SOM × 58% = 17.4 kg carbon
Step 3 – Convert carbon to CO₂ equivalent:
17.4 kg C × 3.67 = 63.9 kg CO₂
Note: Topsoil values are highly variable and depend on actual organic matter content.
Indicative carbon storage result
Indicative carbon storage for topsoil (typical reference value): Approximately 38 kg CO₂ per tonne
How this figure should be interpreted
Carbon storage in topsoil reflects carbon retained within soil organic matter.
It does not represent permanent sequestration, a carbon offset, or net lifecycle emissions. The level of carbon storage depends on soil type, organic matter content, management and use.
Emissions and lifecycle considerations
Emissions associated with soil stripping, screening, blending, transport, placement and any subsequent disturbance are not included in this calculation and must be considered separately when assessing overall environmental impact.
Product-specific notes
Topsoil carbon content varies significantly with land use history, texture, organic inputs and handling. Where project-specific reporting is required, carbon storage should be based on measured organic matter or soil organic carbon testing rather than typical assumptions.
Reference sources
IPCC (2019) – Refinement to the 2006 Guidelines for National Greenhouse Gas Inventories (soil carbon accounting principles; C→CO₂ factor)
FAO – Soil Organic Carbon publications (soil carbon context and variability)
Van Bemmelen factor (SOM→SOC conversion) – widely used soil science conversion (organic carbon ≈ 58% of soil organic matter)
UK DEFRA – GHG reporting guidance (context for carbon communication)
Peer-reviewed literature on soil organic matter, soil organic carbon and stabilisation mechanisms
This document is intended to support informed discussion and responsible material selection.
Good design begins with responsible decisions.
Future landscapes will be judged by today’s actions.