Having just splashed out on a ‘professional’ site design for a new reviews blog, I’ve just spent the best part of half a day re-jigging it to allow me to easily pick up ads from a variety of ad and affiliate networks. I’m suffering a little from the Catch 22 of niche sites. Niches are great, with high conversions and less competition, but also fewer advertisers and less choice of creative.

The original theme was sprinkled with nice looking ad-slots but on closer inspection was pretty useless, with weird sizes like 200×126! I’d need a lot of hours in Photoshop carving up new ads for the site. Banners are pretty poor sales drivers at the best of times, but give a professional look to the site that I was looking for rather than a home-made personal look.

For anyone designing or tinkering with an existing site design the following are the most common sizes that you’ll easily find ads for, and if you’re an advertiser, these are also the slots you’ll find most often on publisher’s sites without having to create bespoke sizes for each site you advertise on.

468×60 banner - the most common, used mainly in page headers just about everywhere. Also one of the worst performing as it tends to get mentally ‘zoned out’ by readers.

120×600 ’skyscraper’ - also very common, running down the side of a page. If you’ve designed a narrow site for 800×600 screens, this can be a useful addition to ‘pad out’ the excessive white space.  These can perform around twice as well as regular banners using almost identical creative. Also available in a 160 pixel wide version which can get your message across better.

125×125 ’small box’ - god only knows who chose this shape, a 120 x 120 would have been far better to match other column widths, but this is used on a lot of blogs as a sponsor’s slot. Stick a couple of them side-by-side over your navigation column without pushing it down too far.

120×60 ‘button’ - not so much an ad as a placeholder for a logo, often used by directory sites as a large alternative to the 88×31 small button. If you’re an advertiser, create at least one that isn’t animated or you’ll make your publisher’s page look like Piccadilly Circus.

728×90 ‘leaderboard’ - Works well across the top of a site but can overtake the site’s own branding as it’s so large. I use a few of these in affiliate sites promoting a single merchant where their branding is stronger than mine.

Other more rectangular formats to hold video and flash are also popular on large media sites, the 300×250 Media Playing Unit is common, however if you are running a very niche site you may find it hard finding advertisers offering these formats.

There are plenty more, but they start to get pretty marginal in the number of advertisers supplying them. A full list is available from the IAB website.