A half, half a or half an

The expressions a half, half a and half an are all completely acceptable.

• Could I have half a pound of oranges? / Could I have a half pound of oranges?
• Joe has half an apple. / Joe has a half apple.

However, expressions like ‘a half a’ and ‘a half an’ are completely unacceptable.

Don’t say or write:

• I have a half an orange.

Note that the expression one and a half is plural.

• I waited for one and a half hours. (NOT I waited for one and a half hour.)

Or you can say: I waited for an hour and a half.