Google CPC (Keyword Tool vs Adsense)

Likely because the GKT is showing what advertisers are paying in the search network (i.e. to have their ads shown on Google SERPs), whereas your site is part of the content network (i.e. Adsense sites), and advertisers pay different prices for both.

If you want to find more accurate CPCs for your adsense site, instead of using the GKT, use the Contextual Targetting Tool (you can find it in the "Tools and Analysis" tab inside the GKT). See if the value it shows there for your KW looks more like what you're really getting.

Just checked Contextual Targeting Tool, the CPC for my keyword is $1.04

I know that the CPC should be less, but the difference is huge.
I have 2 ad units,first ad above the article and the other ad inside sidebar.

Ads are placed in a similar (albeit not exact) way to an auction. The first advert shown on your page (i.e. the one that is highest in your code) will usually show the highest bidder. This bidder may well be paying $1 per click.

If you have two text ad units on your page, then it is likely you have between 5-8 or so adverts being shown at a time. Those that feature below the first advert will likely have a lower bid than the advert shown first.

This means that you should expect a spread of CPC values, with some being lower than the estimated value.

You should also note that Google only pays 68% of the CPC to you, the publisher.

The ads shown may note necessarily be only showing for your exact keyword, it can show for anything you mention on your website.

And finally, use a tool like SpyFu Keyword Spy Tool for Keyword Research | SEO Software & AdWords Tools or http://www.keywordspy.com/ to check how many advertisers there are, and what sort of figures were being paid for the last few month for your keyword. If there aren't many advertisers then you may find that some of the ads being shown on your website aren't even relevant, and will likely come with a much lower CPC.

You can confirm this within your AdSense "Performance Report" - just filter by "Targeting Type".

I take all values of CPC given to me by any report, or any software, with a massive pinch of salt. I usually cut the figure down to just a quarter to give me a more realistic estimate.

Regards
Will

You are better taking the cpc from the contextual targeting tool as this is the display advertisers who are advertising on the content network.

Also consider that Google pays you 68%

Also bear in mind that other related keywords will trigger your ads and they may have lower payouts.

How old is the site? you may find that cpc will increase over time