How this calculator works
This calculator counts the plastic you throw away rather than the plastic you buy, and it uses a typical mass for each item: about 28 g for a one-litre PET bottle, 5.5 g for a shopping bag, 2 g for a food wrapper, 60 g for a detergent bottle and so on. Counts are multiplied by 52 weeks and summed to a yearly mass, then converted to emissions at about 2 kg CO2e per kg of plastic, which covers the oil or gas feedstock, polymerisation and forming. The tree figure divides those emissions by about 21.8 kg of carbon dioxide that a mature tree absorbs in a year, which is the figure used by the United States Forest Service and the Arbor Day Foundation. The estimate leaves out the transport of the finished goods and the methane from plastic that decays in landfill, so the real impact is somewhat higher.
Formula
plastic per year (kg) = sum over items of (items per week x 52 x grams per item / 1000). emissions per year = plastic per year x 2.0 kg CO2e per kg. trees = emissions / 21.8 kg per tree per year.
Worked example
Three bottles, four bags, five wrappers and two takeaway cups a week. Bottles: 3 x 52 = 156 a year, at 28 g each that is 4.37 kg. Bags: 208 at 5.5 g is 1.14 kg. Wrappers: 260 at 2 g is 0.52 kg. Cups: 104 at 12 g is 1.25 kg. The total is 7.28 kg a year, which carries 14.6 kg CO2e, or about 0.67 mature trees for a year.
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Frequently asked questions
Why count weight rather than items?
Weight tracks the resources used and the emissions much better. One heavy detergent bottle can outweigh a hundred straws, and a count of items would hide that. Use the item counts to spot the habit and the weight column to see where the impact is.
Does recycling cancel the footprint?
Only partly. Recycling avoids new resin, but collection, sorting and reprocessing all take energy, and the fibre or polymer usually downgrades. The emissions here are for virgin production, so a recycled item is lower but not zero. Reducing the item in the first place is the larger saving.
What about microplastics?
They are outside this estimate. A plastic item that reaches the environment fragments rather than disappearing, and the mass does not tell you the harm. Reducing single-use items cuts both the carbon and the fragmentation risk.
How can I compare with a national average?
Canadians generate roughly 30 to 40 kg of plastic packaging waste per person a year, though definitions differ. Compare your total with that range and look at the largest line rather than the total alone.
Sources
- OECD (2022): Global Plastics Outlook, economic drivers, environmental impacts and policy options
- Environment and Climate Change Canada: emission factors and reference values for greenhouse gas quantification (national inventory edition, updated annually)
- Environment and Climate Change Canada: plastic waste and pollution reduction