Weird nit to pick. I would probably write "a quarter" as well, but "one-fourth" (or, similarly, "a fourth") sounds pretty normal and idiomatic to me. (Also we

Weird nit to pick. I would probably write "a quarter" as well, but "one-fourth" (or, similarly, "a fourth") sounds pretty normal and idiomatic to me. (Also weird to label something "Americanese", given that out of the countries where English is the primary language, the US is the most populous [unless you count India, which I'm not sure I would]. I'd say that makes us, if not authoritative, at least trend-setting.)