How do we calculate impact?
We track book reuse through recorded deliveries. Environmental estimates are assessed separately.
Methodology version: circular-v1 ·
CO₂e comparison method: carbon-reference-v1
Book weight: an approximate starting model
The general assumption is 250 g per book. AI suggests a format from visible construction: light 150 g, standard 250 g, heavy 450 g. These are not measured catalog averages. Uncertain or mixed sets use 250 g per book. Set quantity is multiplied once. Each listing stores one estimated weight in grams. Reservation and delivery weights are frozen; later listing edits do not change history. This is not a measured weight, saved paper or shipping weight.
How books are counted
Available books are public listings open for reservation. Pending counts exclude cancelled and expired reservations. Delivered counts use valid existing contribution records, with sets counted by their recorded physical quantities. A delivery counts once; a later separate delivery counts again. Marking a book sold without a reservation is not delivery evidence. Each older reservation without a recorded quantity counts as one book.
Period, corrections and personal contributions
Deliveries cover all valid recorded history, including reviewed historical imports. Missing historical records are disclosed separately; an import date is not a delivery date. Account deletion and invalidation can reduce totals. Personal shared and received counts use the existing badge source without changing thresholds. Both participants contribute to the same delivery, so personal totals must not be added to calculate community impact. Two historical completed transactions use an assumption of one book and 250 g each.
Paper content, not paper saved
For inner pages: pages ÷ 2 × page area (m²) × grammage (g/m²) ÷ 1000. Covers, glue and board books require separate assessment. Every book in a set needs data. The catalog lacks sufficient measurements, so we do not publish kilograms. This is not paper saved or trees saved. Repeated deliveries represent material circulating in each transfer, not unique material stock.
CO₂e: a production reference comparison
Calculation: estimated delivered book weight (kg) × 2.32 kg CO₂e/kg. Reference: VTT (2010), a 500 g Finnish hardcover at 1.16 kg CO₂e. The scope runs from raw materials to the retailer. Linear scaling by mass is our comparison assumption, not a current Dutch children’s-book average. We assume no measured displacement of new purchases. Reuse delivery, packaging and additional operations are not deducted, so this is not net savings. Only valid deliveries count; separate later deliveries count again. Method: carbon-reference-v1.
What we do not claim
This is not KitapBuurt’s corporate carbon inventory or an independent sustainability certification. The production equivalent cannot be deducted from the company footprint. Badges recognize sharing activity. Sources, version, scope and assumptions are disclosed here; missing records are not presented as zero data.
How do we compare book prices?
The difference is the total new-copy reference price minus total second-hand book cost for eligible deliveries with price data. The percentage uses the reference sum for the same group. Set prices count once; free books count and negative differences remain. Prices are seller declarations. New reservations freeze the reference price. Historical comparisons freeze the current seller reference at rollout only when set quantities match. Missing prices and shipping are excluded. This comparison does not assume a new purchase would have occurred.