The best Adsense ad unit sizes for maximum income

When you sign up for Google Adsense, and you go to try and customize your ads, you get faced with a pretty big selection of ad types/sizes/shapes from which to choose. Which one will get you the highest click-through rating? Will one get you a higher cost per click? Which ones are absolutely worthless? Well, there's easy answers to that, and really, you know what your first instincts are telling you. Chances are, your first instincts are probably right.

There are five types of ad units that I consider to be worthwhile. As far as I'm concerned, the other ones aren't even worth using. And in order, not only do I consider them to be worthwhile, but testing and experience prove me right.

NUMBER ONE: 336x280. The "large rectangle". This has proven time and time again, with many an Adsense user, to be the highest-performing ad unit. Why? It draws attention. It shows four ads at a time, with a good sized font. It takes up a lot of real estate, but if you want a high CTR, it's worth it. And it's one of the most widely used, too, therefore the chance that advertisers will specifically target those MORE, is higher.

NUMBER TWO: 300x250. The "medium rectangle". It's right up there with the first one. It's wide, it's taller than a banner, and it's easily targetable. It takes up just slightly less real estate than the large rectangle, but with it, you will usually show the same ads, just with slightly smaller fonts. Four ads is the norm for this type of unit.

NUMBER THREE: 250x250. The "large square". Again, it's got that balance of height and width. This particular one shows three ads, so if you want to keep down the number of ads you show on a page, mix this unit in with the other ones. Its balance of height and width is great for maximizing visibility and drawing attention to the ads, and it makes it very versatile - you can stick it at the top of the page, bottom of the page, sides, and inside content, too.

NUMBER FOUR: 160x600. The "wide skyscraper". This one will show more ads than any other unit: usually 5 or 6 ads. Unlike the other ad units, this one is not very versatile - stick it either at the left side of the page, or right side of the page, because this one won't look good anywhere else. However, it is quite visible if you stick it on the left side of the page (not so much the right), and will get a real nice CTR going. Your CPC can tend to lower, though, if you use this combined with other large units, because of the sheer quantity of ads your site will run. However, it is still one of the best units.

NUMBER FIVE: 728x90. The "leaderboard", or basically, a gargantuan banner ad. There is only one worthwhile place to put this particular ad, and that is below the title. Putting this at the bottom of the page will yield a low CTR, and a low CPC, all in one, making it virtually worthless down there. Below the title, this will get a nice CTR going, but in my experience, not as good as a rectangle or a large square will - in fact, less than half of the CTR. This, like the last one, usually shows 5 ads.

As far as I'm concerned, the smaller 1-2 ad blocks and the 468x60 banner are virtually worthless, unless combined with another ad unit at the top of the page to make an irregular ad block (I particularly like to mix the vertical banner - 120 x 200 - with the 250x250 large square. I get good results off of that without making my sites look spammy). You'd be well off ignoring any of the ad units I haven't listed, but ultimately, it's your call. And after some experimenting, you may find that something else works better for you. But most likely, the 1-2-3-4-5 I've listed here will be top earners for you, either in that exact order, or almost in that exact order.