There are standard sizes (measured in pixels) for static, animated and rich media
banner adverts. Creating banners in these sizes means the ads can be placed
on many websites (advertisers sell space in these sizes as well). And here, size
(both dimensions and file size) does matter – you can expect varying rates of
clickthroughs and conversions across the range of sizes. Bigger is usually better,
but if you want to know what works best for your brand, test.