Reduce your plastic

Negative counts and values that are not a number fail with invalid_input and are not billed.

What plastic avoided means and how weekly counts become kilograms

Each count is multiplied by a published empty-item mass in grams that the endpoint documents and does not let you override: twelve point five grams for a typical five-hundred-millilitre PET beverage bottle, six grams for an HDPE grocery bag, zero point four two grams for a polypropylene drinking straw, eight grams for a disposable polypropylene or polystyrene cold cup, twenty-two grams for a polypropylene takeaway clamshell, and three grams for one polypropylene utensil. Annual kilograms — the primary result annual_plastic_kg — equal annual grams divided by one thousand. The breakdown lists every category with its weekly count, grams each, weekly grams, and annual kilograms so you can see which swap actually moves the needle. largest_source names the heaviest category when the yearly mass is positive; that field is omitted when every count is zero.

Input contract, aliases, and why a negative or non-numeric count fails

A value that is not a number — for example the word seven, an object, or NaN — is likewise rejected because a count must be a finite number. Zero is valid on every field and contributes nothing to the yearly mass, which is the correct result for a category you already do not use. POST a JSON body with six required finite numbers: bottles, bags, straws, cups, containers, and cutlery, each a weekly count of items you are swapping. Accepted aliases for bottles are bottles_week, plastic_bottles, weekly_bottles, bottle_count, and n_bottles. Bags accept bags_week, plastic_bags, weekly_bags, bag_count, and n_bags. Straws accept straws_week, plastic_straws, weekly_straws, straw_count, and n_straws. Cups accept cups_week, plastic_cups, weekly_cups, cup_count, and n_cups. Containers accept containers_week, plastic_containers, weekly_containers, container_count, and n_containers. Cutlery accepts cutlery_week, plastic_cutlery, weekly_cutlery, cutlery_count, and n_cutlery. Each field may arrive as a JSON number or as a decimal numeric string. Missing fields, empty strings, booleans, non-finite values, and magnitudes beyond the supported absolute ceiling fail with invalid_input naming the field. Any negative count is rejected with a message that the field cannot be negative: a weekly usage cannot be a sink, and the request is not billed. On success the body echoes the cleaned weekly counts, reports weeks_per_year as fifty-two, weekly_plastic_g, annual_plastic_g, annual_plastic_kg as the primary yearly mass in kilograms, items_swapped_per_year as the sum of the six counts times fifty-two, and a breakdown of six records with item, weekly_count, grams_each, weekly_g, and annual_kg. formula and equation restate the identity for display. Pair the kilograms with your own recycling or reusable-manufacturing notes if a protocol requires them; this endpoint reports avoided single-use mass only.

Where a reduce-your-plastic calculator earns its keep

Household waste-reduction challenges and office green-team dashboards use a reduce-your-plastic calculator so a weekly tally of bottles, bags, straws, cups, containers, and cutlery becomes a yearly kilogram figure they can drop into a pledge board without opening a spreadsheet of unit conversions. Failed validation does not consume balance. Classroom environmental-science labs and exam-prep generators need a deterministic oracle that rejects a negative straw count as invalid_input instead of silently returning a negative mass that a buggy grader might treat as a credit. Cafe and takeaway operators who replace plastic cups and cutlery often want to quote annual kilograms avoided for a staff of a given size; calling a tiny parse API avoids pulling a desktop workbook every time headcount changes. Keep requests small, pin the rounded annual_plastic_kg and breakdown rows in tests, and you get reproducible plastic-avoidance estimates for homework, LMS plugins, sustainability scripts, and edge workers without standing up life-cycle software of your own. Use fifty-two weeks as the year length this endpoint documents; if a protocol uses three hundred sixty-five days, scale the yearly mass afterwards rather than asking the calculator to invent a calendar.