Methodology v1.2
The formula, published in full
A score is only useful if you can reproduce it. This page contains the arithmetic, the factor table and the rules that decide how much we trust an input.
1. The formula
net_co2e = (material_factor × mass_kg)
+ packaging_factor
+ (transport_factor × tonne_km)
− recyclability_credit
tonne_km = (mass_kg ÷ 1000) × distance_km
credit = net_co2e × 0.15 (recyclable packaging only)
GIS = clamp(0, 100, 100 − (net_co2e ÷ category_baseline) × 62)The category baseline is the modelled impact of a conventional equivalent product in the same category. Scores are therefore comparable within a category and should not be compared across categories.
2. Confidence tiers
Every score carries a tier describing the provenance of its inputs. The tier never gets upgraded without new evidence.
Inputs corroborated by third-party documentation — mill certificates, weighbridge records or lab reports held on file.
Inputs supplied by the artisan partner under a written declaration, spot-checked against category norms.
Inputs modelled from category defaults where primary data is not yet available. Treated as provisional.
3. Emission factor table
The live factor set for methodology v1.2. Each row cites its source.
| Factor | Category | Unit | kg CO₂e | Water L | Plastic g | Source |
|---|---|---|---|---|---|---|
Air freight (international) log_air_intl | logistics | tonne-km | 0.602 | 0 | 0 | GLEC framework v3 air factors |
Road freight (India, domestic) log_road_in | logistics | tonne-km | 0.107 | 0 | 0 | GLEC framework v3 road factors |
Bamboo mat_bamboo | material | kg | 0.31 | 75 | 0 | Bamboo LCA, INBAR 2022 |
Beeswax mat_beeswax | material | kg | 1.1 | 340 | 0 | Apiculture LCA meta-analysis |
Conventional cotton mat_conventional_cotton | material | kg | 5.9 | 9800 | 0 | Textile Exchange LCA 2024 |
Jute mat_jute | material | kg | 0.65 | 320 | 0 | FAO jute LCA meta-analysis 2023 |
Organic cotton mat_organic_cotton | material | kg | 3.8 | 2100 | 0 | Textile Exchange LCA 2024 (organic, rain-fed share adjusted) |
Reclaimed mango wood mat_mango_wood | material | kg | 0.42 | 90 | 0 | Reclaimed-timber factor, ecoinvent-derived |
Recycled brass mat_brass_recycled | material | kg | 2.4 | 260 | 0 | Secondary copper-alloy factor, IPCC-consistent |
Recycled glass mat_glass_recycled | material | kg | 0.85 | 120 | 0 | DEFRA 2024 (cullet-fed container glass) |
Recycled paper / board mat_recycled_paper | material | kg | 0.72 | 210 | 0 | DEFRA 2024 conversion factors (closed-loop paper) |
Soy wax mat_soy_wax | material | kg | 1.45 | 780 | 0 | Vegetable-oil derivative factor |
Stainless steel mat_stainless_steel | material | kg | 6.15 | 480 | 0 | World Steel LCI 2023 |
Terracotta / fired clay mat_terracotta | material | kg | 0.88 | 140 | 0 | Indian kiln survey averages (CSE 2023) |
Virgin brass mat_brass_virgin | material | kg | 8.1 | 640 | 0 | Primary copper-alloy factor |
Virgin polypropylene mat_virgin_plastic | material | kg | 3.2 | 180 | 1000 | PlasticsEurope eco-profile |
Corrugated board box pack_corrugate | packaging | unit | 0.19 | 46 | 0 | DEFRA 2024 packaging factors |
Plastic film / laminate pack_plastic_film | packaging | unit | 0.14 | 9 | 22 | PlasticsEurope + weight survey |
Recycled paper wrap pack_paper_wrap | packaging | unit | 0.06 | 18 | 0 | DEFRA 2024 packaging factors |
Reusable cloth pouch pack_cloth_pouch | packaging | unit | 0.11 | 210 | 0 | Cotton pouch, amortised over 8 declared reuses |
4. Version history
Current version. Adds last-mile delivery, return logistics and the vision-verification cross-check.
- Last-mile delivery now in scope (previously excluded)
- Return logistics modelled at category-level return rates
- Packaging declaration cross-checked against product photography
- Anomaly detector flags declared-vs-detected material mismatches before publish
- Published the full factor table with source attribution
Added water and plastic tracking, plus the three-tier confidence rating.
- Introduced water (litres) and plastic (grams) as first-class metrics
- Added confidence tiers: Verified / Supplier-Declared / Estimated
- Corrected cotton water factor after review of the CSE 2024 dataset
- Recyclability credit capped at 15% of gross score
First public release of the Green Impact Score. Materials, packaging and logistics only.
- Initial materials emission-factor table (14 factors)
- Packaging scored as a flat penalty per material class
- Logistics limited to first-mile road freight
Our change-control rules live in methodology versioning. To score a hypothetical product yourself, use the impact calculator.