Reusable Bag Break-Even Calculator
How many uses it takes for a cotton tote, a woven polypropylene bag or a bag-for-life to have a lower climate footprint than the single-use plastic bags it replaces — and how long that is at your shopping rate.
A thin single-use plastic bag has a tiny footprint — a few grams of CO₂e — because there is so little of it.
How the reusable bag break-even calculator works
A thin single-use plastic bag has a tiny footprint — a few grams of CO₂e — because there is so little of it. A reusable bag costs far more to make, so it only wins once it has replaced enough single-use bags: about 4 uses for a thick bag-for-life, 11 for a woven polypropylene bag and over 130 for a cotton tote, by the UK Environment Agency’s life-cycle study. Divide by how many bags you use a week for the time to break even.
Formula: break-even uses = reusable bag footprint ÷ single-use bag footprint
Worked examples
| Inputs | Uses to break even | Note |
|---|---|---|
| Cotton tote, 4 bags a week | 134 | 134 uses — about 8 months |
| Woven polypropylene bag | 11 | 11 uses |
| Bag-for-life | 4 | 4 uses |
FAQFrequently asked questions
Why is a cotton bag so high?
Growing cotton takes water, fertiliser and land, and a tote weighs 100–200 g against 6 g for a thin plastic bag. Several life-cycle studies put a cotton bag at 130 to several thousand uses depending on which impacts are counted; climate alone gives the lower figures used here.
So should I use plastic?
The climate footprint is only part of it — litter and marine plastic are the reason single-use bags are banned in many places. The practical answer is any bag you will actually reuse for years, and never a new tote for every shop.
What if I reuse single-use bags as bin liners?
That is a second use, which roughly halves their footprint per use and raises the break-even for the reusable bag. Enter 3 g for the single-use bag to approximate it.
Where do the figures come from?
The UK Environment Agency’s 2011 life-cycle assessment of carrier bags gives the use counts (4, 11, 131); the gram figures here are those counts scaled to a 6 g single-use bag. A Danish 2018 study found higher counts across more impact categories.
Where these figures come from
- UK DESNZ / DEFRA — Greenhouse gas reporting: conversion factors — the flight, fuel and waste emission factors used here
- Scarborough et al. (2014), Climatic Change — Dietary greenhouse gas emissions — the per-diet daily emission figures
- US EPA — Technical Assistance Document for the Reporting of Daily Air Quality (AQI) — the PM2.5 breakpoints the air quality calculator uses
- US EPA — Greenhouse Gas Equivalencies Calculator — the official US equivalency factors
Last checked: September 2026. Factors are taken from published government and peer-reviewed sources, each named on the page with its year.