All Facebook Image Dimensions and Ad sizes 
Why Custom Audience is the Most Powerful Strategy in Facebook Ads
Facebook is always changing and improving. When this happens, advertisers need to ensure that they are following every new rule that Facebook introduces.
Did you know that Facebook has recently updated their image dimensions and ad sizes? This is something you need to pay attention to.
Targeting is very important in online marketing — so important that if you fail to target your audience properly, you are likely to fail in any of your ad campaign, because targeting the wrong group of people is pointless and a waste of of time. People who cannot relate to your business offers will not engage with you, hence they will not buy from you either.
Custom audience will help you find leads and create sales conversions. It will also help you understand your customers better. That way you will be able to craft better ad campaigns in the future.