carry coals to Newcastle
to take something to a place or a person that has a lot of that thing already

[TahlilGaran] Dictionary of Contemporary English ▲

carry coals to Newcastle
carry/take coals to Newcastle
[British]
to take something to a place or a person that has a lot of that thing already.
Exporting pine to Scandinavia is a bit like carrying coals to Newcastle.

[TahlilGaran] English Idioms Dictionary ▲

carry coals to Newcastle
to bring something of which there is plenty, to duplicate something (Newcastle is a town in England where there is a lot of coal)
Bringing extra food to the farmer's picnic was like bringing coals to Newcastle.

[TahlilGaran] English Idioms Dictionary ▲

carry coals to newcastle
v. phr. To do something unnecessary; bring or furnish something of which there is plenty.
The man who waters his grass after a good rain is carrying coals to Newcastle.
Joe was carrying coals to Newcastle when he told the doctor how to cure a cold. (Newcastle is an English city near many coal mines, and coal is sent out from there to other places.)

[TahlilGaran] English Idioms Dictionary ▲