Preset values are study-specific. Edit these only when you have better product or local data. CO2e means carbon-dioxide equivalent.
These examples reproduce the UK Environment Agency study's no-secondary-reuse climate comparison after allowing for each bag's carrying capacity. Values are rounded, so the calculator may show an extra decimal place.
A smaller-capacity PP bag, washing, or loss raises the count; a larger capacity lowers it.
Washing raises the count. Reusing HDPE bags as bin liners also raises it because a separate liner is avoided.
This is a hypothetical reuse result: moisture and tearing may prevent a paper bag reaching the required uses.
Effective alternative manufacturing CO2e = preset manufacturing CO2e / (1 - loss rate)
Net avoided CO2e per alternative use = (bags replaced x displacement x current bag CO2e after secondary-reuse credit) - care CO2e
New-bag break-even uses = effective manufacturing CO2e / net avoided CO2e per alternative use
Annual alternative uses = current bags per year x coverage / bags replaced per alternative use
Annual current bags avoided = alternative uses x bags replaced x displacement
Two different views: “New purchase today” counts the upfront footprint of each bag needed across the chosen horizon. “Steady-state annual allocation” spreads manufacturing across expected uses. If you already own the bag, its first manufacturing impact is sunk in the forward-looking result; later replacements are counted only after its expected uses are exhausted.
If avoided emissions per use are zero or negative, break-even is impossible under the selected assumptions. That can happen when capacity or displacement is low, secondary reuse gives the current bag a large credit, or care emissions are high.
Preset set UK-DK-2026.1, calculator method v2.0.0. Footprints below are calculated values taken from, or derived directly from, the named bag-specific LCA tables. They are not generic material emission factors. Selecting a preset shows its source beside the control.
| Preset | Material | Weight | Footprint | System boundary | Geography / reference year | Direct source |
|---|---|---|---|---|---|---|
| Single-use HDPE | Virgin HDPE blend | 8.12 g | 25.35 g CO2e | Cradle-to-grave, no primary or secondary reuse; 2.082 kg CO2e / 82.14 bags | UK; bags available 2006, study published 2011 | UK Environment Agency, Tables 3.1 and 6.1 |
| Reusable LDPE | Virgin LDPE blend | 34.94 g | 114.11 g CO2e | Cradle-to-grave, no primary reuse; 6.924 kg CO2e / 60.68 bags | UK; bags available 2006, study published 2011 | UK Environment Agency, Tables 3.1 and 5.5 |
| Non-woven PP | Virgin polypropylene with PP/cotton thread | 115.83 g | 325.28 g CO2e | Cradle-to-grave, no primary reuse; 21.510 kg CO2e / 66.13 bags | UK; bags available 2006, study published 2011 | UK Environment Agency, Tables 3.1 and 5.6 |
| Paper | Virgin kraft paper | 55.20 g | 85.00 g CO2e | Cradle-to-grave, no primary reuse; 5.523 kg CO2e / 64.98 bags | UK; bags available 2006, study published 2011 | UK Environment Agency, Tables 3.1 and 5.4 |
| Conventional cotton | Woven conventional cotton | 183.11 g | 5,955.98 g CO2e | Cradle-to-grave, no primary reuse; 271.533 kg CO2e / 45.59 bags | UK use; cotton model 2000–2005, study published 2011 | UK Environment Agency, Tables 3.1 and 5.9 |
| Organic cotton | Organic cotton | 252 g | 5,400 g CO2e | Production only; published production score for one bag | Danish market 2017; European production model, published 2018 | Danish EPA, Table 2 and Table 19 |
| Custom / other bag | User supplied | User supplied | User supplied | Must match the comparison purpose | User supplied | Enter and document your product or supplier source |
Boundary warning: The organic-cotton preset uses a production-only score because that is the directly tabulated per-bag result. Do not treat a mixed-boundary comparison as a certified comparative LCA. Enter product-specific cradle-to-grave values for procurement claims.
Primary references: UK Environment Agency carrier-bag LCA (published 2011); Danish EPA grocery-bag LCA (2018); and the UNEP Life Cycle Initiative meta-analysis (2020).
The best practical choice is usually a bag you already have, can fill efficiently, and will reuse many times. Climate impact is not the same as overall environmental impact.
| Material | Typical durability | Climate break-even in cited studies | Other important impacts | End-of-life | Major caveat |
|---|---|---|---|---|---|
| HDPE | Light; sometimes reused | Reference bag | Litter and fossil feedstock are not represented by CO2e alone | Film recycling varies locally; useful secondary reuse may avoid liners | Taking more bags or losing secondary reuse changes the comparison |
| LDPE | Moderate, designed for reuse | About 4–5 UK-study uses vs HDPE | Heavier plastic use | Recycling acceptance varies | Capacity and thickness vary widely |
| Non-woven PP | Often tens of uses if kept | About 11–14 UK-study uses vs HDPE | Fossil resources and possible fibre shedding | Specialist recycling may be limited | Loss before repeated use erodes the benefit |
| Paper | Low to moderate; moisture-sensitive | About 3–4 hypothetical UK-study uses vs HDPE | Forestry, water, eutrophication, and heavier transport | Widely recyclable when clean and dry | The required reuse may not be physically realistic |
| Cotton | High when well made | About 131–173 UK-study uses vs HDPE | Water, land, fertiliser, toxicity, and eutrophication can dominate | Textile routes vary; repair extends life | Bag weight and agricultural model strongly affect results |
| Organic cotton | High when well made | Study- and boundary-specific; use calculator cautiously | No synthetic pesticides, but lower yields can increase land and resource demand | Textile routes vary | Organic does not guarantee lower impact in every category |
Bag weight and carrying capacity matter because the fair comparison is the same shopping carried home, not simply one bag versus one bag. Litter, toxicity, water use, biodiversity, microplastics, and local disposal can change the conclusion even when one option has lower modeled CO2e.
There is no universal number. In the UK Environment Agency study, the conventional cotton bag needed about 131 shopping uses against an HDPE bag with no secondary reuse, or 173 uses when 40.3% of HDPE bags were reused as bin liners. Bag weight, capacity, geography, and lifecycle boundary can change the result.
Against an HDPE bag with no secondary reuse, the UK study reported about 11 uses for non-woven polypropylene, 3 for paper, and 4 for reusable LDPE. With 40.3% bin-liner reuse of HDPE, those figures became 14, 4, and 5. These are study-specific, not universal targets.
Sometimes for a particular impact and scenario, but not automatically. Paper is heavier, may need reuse to offset production, and performs differently for water, land, toxicity, recycling, and disposal. Capacity and whether it survives reuse matter.
Studies use different bag weights, carrying capacities, energy systems, transport distances, disposal routes, secondary reuse assumptions, impact methods, geographies, and years. Compare the functional unit and system boundary before comparing a reuse number.
Yes. Washing adds care emissions per use and can delay break-even. If care emissions equal or exceed the avoided emissions per reusable use, climate break-even is impossible under those assumptions.
Yes. Secondary reuse can avoid production of a separate bin liner, reducing the disposable bag's net footprint and making an alternative bag take longer to break even. Only claim the credit when a liner is genuinely displaced.
Usually, keep using a serviceable bag you already own. Its production impact is sunk for the forward-looking decision, while buying a replacement creates a new manufacturing impact. Replace it when it is no longer safe or functional.
No. CO2e is only one environmental indicator. This calculator does not quantify litter, marine harm, microplastics, toxicity, biodiversity, or local water stress, so the lowest-carbon option is not automatically best overall.
Author: Starlight Tools Environmental Calculators Desk. Qualified independent calculator reviewer: not yet appointed. Review date: July 16, 2026. Method version: 2.0.0.
Included stages: exactly the lifecycle stages included in each selected preset, plus user-entered care and an optional secondary-reuse credit. UK presets cover raw materials, manufacture, primary packaging, distribution, and modeled disposal; consumer travel is excluded. The organic-cotton preset is explicitly production-only. Calculated claims: break-even, avoided bags and mass, annual/horizon CO2e, per-use comparison, and costs. Source claims: preset weights, footprints, boundaries, publication details, and study-specific reuse figures.
This is a screening calculator, not a certified comparative LCA. Product-specific decisions should use matched system boundaries, current supplier data, local disposal, measured reuse, and professional review.