The adjective use of a couple, without of, has been called nonstandard, but it is not. In both British and American English it is standard before a word (as more or less) indicating degree <a couple more examples of Middle English writing — Charles Barber>. Its use before an ordinary plural noun is an Americanism, common in speech and in writing that is not meant to be formal or elevated <the first couple chapters are pretty good — E. B. White (letter)><still operated a couple wagons for hire — Garrison Keillor>. It is most frequently used with periods of time <a couple weeks> and numbers <a couple hundred><a couple dozen>.