Canada made the inch fit the millimetre

A sheet of North American Letter paper is 8½ by 11 inches. In exact metric terms, that is 215.9 by 279.4 millimetres.

Canada once had a cleaner answer: 215 by 280 millimetres.

In 1976, during metric conversion, the Canadian General Standards Board introduced a series of correspondence-paper sizes called P1 through P6. P4 was the office sheet. It was not international A4, which measures 210 by 297 millimetres. It was Letter paper rounded to the nearest five millimetres.

The same operation was performed on larger American sizes. Ledger, 11 by 17 inches, became P3 at 280 by 430 millimetres. The result looked metric in a procurement specification without requiring desks, files, envelopes, printing equipment and habits to become European.

This preserved the awkward part too. A4 belongs to a series built around one proportion: cut a sheet in half and the two smaller sheets have the same shape. The P series inherited the alternating proportions of the American sizes. It used millimetres but not the geometry that makes the international system useful.

The standard lasted surprisingly long. “Paper Sizes for Correspondence” was still listed in the federal standards catalogue in 2011, shortly before Canada’s custom paper-size standards were withdrawn in 2012. Ordinary Canadian paper meanwhile remained ordinary Letter.

Metrication is often described as replacing one measurement system with another. P4 shows a cheaper option. Keep the object, move its edges by less than a millimetre, and give the compromise a new name.