Will a 12cm cpu cooler fit a 18.3cm case?

Perhaps if you told us what case it is and tell us where abouts you want to fit the fan...

Can you please mention the case and cpu cooler so that I would get a better idea.

it might/should fit,most case are a standard width ,but if you are looking for ultimate cooling i would suggest a bigger case, as the link is showing a micro-atx case ,not much space in them for moving air for effincent cooling

Yes, I know:( I didn't realise when I built the rig that the case would be a problem as it was my first build... Was a very bad decision to go for a cheap case, However I might invest in a haf series case which are meant for high air flow, But it means taking apart and rebuilding the rig facepalm.

Thank you for your inputs though.