The Schoolbag Experiment

Mikołaj (my awesome son) is in the fourth grade. This year starts a new subject called “Nature Studies”, which includes basic research methodology. Amid the recurring national debate regarding the excessive weight of school backpacks, I decided to run an experiment for my child’s homework: weighing every single item in the backpack to find out which item weighs the most — and therefore, which subject is “heaviest”.

Weighing

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The raw data is available in CSV format on GitHub.

Total weight: 8498g (~8.5 kg).

Notebooks

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The first thing that stood out was the huge variance among 60-page notebooks:

The Nature notebook (the outlier above the 60-page cluster) had a hardcover, similar to the Technology spiral notebook with 100 pages and heavy cardboard covers (which alone weighed half a kilogram (!)). First takeaway: avoid hardcovers and spiral notebooks; substantial weight can be saved right here.

Accessories

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How much do the stationary accessories weigh?

Fixed overhead comes out to 1450g — reasonable.

Textbooks

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Now the core question: how much do textbooks weigh per subject?

The results are clear: the heaviest subject is not math, but Polish, where 3 books (2 textbooks and 1 workbook) alone weigh 1.5kg. Add the backpack and pencil case, and that’s 3kg. If Nature lands on the same day, we hit 4kg — dangerously close to the maximum recommended limit for a fourth grader.

Noticeably absent: Computer Science (IT), which weighs a solid 0g (no textbook, no workbook).

Can we stay under 6kg per day?

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Based on the weekly class schedule, the daily backpack load is:

Health guidelines suggest that a child’s backpack should not exceed 10–15% of their body weight. For 9-year-olds (averaging 25–41 kg), this corresponds to a maximum safe weight between 3.75kg and 6.15kg.

In practice, without lockers or schedule optimization, daily bags regularly breach the recommended safety thresholds.