All online advertisements are measured in pixels. This is a standard measurement that all designers are able to work with. Online advertising is measured horizontal x vertical (opposite to print adverts).
Banner(468x60)
Sky(120x600)
MPU (300 x 250px)
Mini Banner (300 x 100px)
Creatives can be supplied as a GIF, JPEG or Flash (swf). Flash adverts will need a back up GIF or JPEG. Flash adverts will also need a ClickTag – this is a technical term that Flash designers will be aware of, and allows the advert to click through to the advertisers website.