How this calculator works
The calculator turns a weekly habit into a yearly weight for each item, uses typical masses (28 g for a PET bottle, 5.5 g for a bag, 12 g for a takeaway cup, 0.5 g for a straw), and takes the difference between the current and goal counts. The savings are shown in kilograms of plastic and in carbon dioxide equivalent at 2 kg CO2e per kg of virgin plastic. The table shows which items carry the saving, which is the point: replacing a few heavy bottles beats giving up hundreds of light straws. Reductions are not additive across households unless everyone makes them, so treat the result as one person's contribution.
Formula
plastic per year for an item (kg) = (count per week x 52 x grams per item) / 1000. saved per year = sum of (now per year minus goal per year) across items. emissions saved = saved plastic x 2.0 kg CO2e per kg. reduction (percent) = saved / current x 100.
Worked example
Three bottles a week reduced to one, and four bags reduced to two. Bottles: 156 a year at 28 g falls to 52 a year, saving 104 x 28 g = 2.91 kg. Bags: 208 at 5.5 g falls to 104, saving 104 x 5.5 g = 0.57 kg. The two changes save 3.48 kg of plastic and 6.97 kg CO2e a year, a 63 percent cut on those items alone.
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Frequently asked questions
Which items should I target first?
Bottles, detergent bottles and cups carry the most weight per item, so each one you avoid saves the most plastic. Straws and swabs feel symbolic but weigh almost nothing. A refillable bottle used daily is usually the largest single change.
Is a glass or metal bottle better than plastic?
It depends on how often you use it. A stainless steel bottle has a much larger manufacturing footprint than a PET bottle, but it pays back after a few dozen uses. The break-even is well within a year for regular users.
Does the goal have to be zero?
No. Going from three bottles a week to one is a bigger practical saving than failing to reach zero. The calculator shows the saving for any goal, so set one you will keep.
What about recycling my remaining plastic?
Keep recycling what you still use, but count the saving here as avoided production, not as recycling. Recycling recovers some material and energy; it does not remove the original manufacturing emissions.