Every office eventually asks the same question: how much shelf do the files actually need? The answer is more computable than most furniture questions, because three of its inputs are fixed by law and by DIN format. This article walks through the calculation, from retention periods to binder measurements to running metres, so the shelving decision becomes arithmetic instead of estimate. It describes the German rules; the logic transfers, the numbers may not.
What must be kept, and for how long
German commercial and tax law sorts business paper into three retention classes. Accounting records (invoices, bank statements, receipts) must be kept for eight years; this was shortened from ten by the Fourth Bureaucracy Relief Act and applies since 2025. Annual financial statements, opening balances and inventories stay at ten years. Commercial and business letters, sent and received, keep six years. In every case the clock starts at the end of the calendar year of the last entry, which is why archives thin out neatly by year-end: at the start of 2026, accounting records through 2017 can go.
Two practical notes belong beside the law. First, these are minimums, and documents relevant to open proceedings or audits keep beyond them. Second, the rules govern the documents, not the medium – digitised archives under proper procedures shrink the paper problem at its root. What follows applies to whatever paper remains, and in most offices that is still a wall's worth.
The binder arithmetic
The A4 lever-arch binder is a standardised object: about 32 cm tall, 28.5 cm deep, with spines of 80 or 50 millimetres. That yields the three numbers every shelf plan needs. Per running metre, about twelve wide binders stand comfortably with browsing slack. A full wide binder weighs around two to two and a half kilograms, so a metre of full binders comes to roughly 25 to 30 kilograms. And the shelf level itself needs about 35 cm of clear height and at least 29 cm of depth so binders stand fully supported without overhanging.
Now the volume estimate. Count the binders the business fills per year, a number most small offices know instinctively, and multiply by the retention years that apply to their contents. A practice filling twenty accounting binders a year, kept eight years, carries 160 binders at steady state: a touch over thirteen running metres, before adding the ten-year and six-year classes and the working files that never leave the desk's reach. Steady state is the useful concept here: after the first full cycle, one year's worth enters and one leaves, and the archive stops growing.
