Our methodology: How we calculate your impact
We show your impact as a simple, human metric. Under the hood, it is avoided impact from new production, calculated from a new item footprint and a replacement rate.
1) What your impact means
Your impact = the water and CO₂ that would have been used to make a comparable new item, adjusted by how often pre owned purchases replace new purchases, then summed across your sales or buys.
2) What is included, what is not
- Impact of producing a comparable new item, by category or item study
- Replacement rate for resale, applied to each pre owned sale
3) Where our numbers come from
Method and market factor we use WRAP's published methodology for displacement. In our data, we use a replacement rate of 0,646
Footprints for "a new item". Circular pairs WRAP's method with the best available item level Life Cycle Assessment (LCA) for each representative category, for example Levi's jeans LCA.
In short: WRAP gives the method and default rate, reputable LCAs give the per item footprint.
4) Constants for communication
Trees planted
1 tree equals 21 kg CO₂ absorbed over time, used only as a simple equivalent
Year of drinking water
1 person year equals 1 000 liters, used only as a simple equivalent
5) Formulas
Step 1, Savings from new production avoided
Water Saved (L) = Water Footprint New item (Liters) × Number of items in that category Sold
CO2 Saved (KG) = CO2 Footprint New Item (KG) × Number of items in that category Sold
Step 2, apply the replacement rate to estimate avoided impact
Net Water Saved (L) = Water Saved (L) × 0,646
Net CO2 Saved (KG) = CO2 Saved (KG) × 0,646
Step 3, show the two simple equivalents
Trees Equivalent = Net CO2 Saved (KG) ÷ 21
Drinking Water = Net Water Saved (L) ÷ 1 000
6) Example with actual jeans numbers
Assume your store sells 1 000 pre owned pairs of jeans
New item footprint
33,4 kg CO₂ per pair, 3 781 L water per pair
Total impact of producting 1 000 new pair of jeans
33 400 kg CO₂, 3 781 000 L water
Apply WRAP replacement rate 0,646
- Net CO₂ saved, 21 580 kg (rounded)
- Net water saved, 2 443 000 L (rounded)
Equivalents
- Like planting 1 028 trees (21 580 ÷ 21)
- Full year of drinking water for 2 443 persons (2 443 000 ÷ 1 000)
Your Impact: You saved 21 580 kg CO₂ and 2 443 000 L of water, like planting 1 028 trees and supplying a full year of drinking water for 2 443 persons
7) How we show it in product
- Primary numbers, kilograms of CO₂ saved and liters of water saved
- One CO₂ equivalent, like planting X trees
- One water equivalent, full year of drinking water for X persons
8) Rounding
Water
- nearest 10 below 10 000 L
- nearest 100 from 10 000 to 999 999 L
- nearest 1 000 at 1 000 000 L and up
CO₂
- nearest 1 below 1 000 kg
- nearest 10 from 1 000 to 99 999 kg
- nearest 100 at 100 000 kg and up
Equivalents, whole numbers, minimum 1
9) Sources
WRAP, Displacement Rates Untangled methodology and UK survey results, default resale displacement used: 0,646
https://www.wrap.ngo/resources/report/displacement-rates-untangledWRAP, Valuing Our Clothes, The Cost of UK Fashion (2017) sector footprints and method context
https://www.wrap.ngo/resources/report/valuing-our-clothes-cost-uk-fashionLevi Strauss & Co., The Life Cycle of a Jean item LCA used for jeans footprints
https://levistrauss.com/wp-content/uploads/2015/03/Full-LCA-Results-Deck-FINAL.pdfQuestions about our methodology? Ask us anything at hei@getcircular.ai