This site will show you what Google's Adsense will look like when you pace their code on your website, hence, adsense preview.
This tool was one of the first on the web to show you what you can expect from Adsense Ads, but now, Google offers a far superior tool with a ton of options.
Take some time and visit the adsense preview tool and see what to expect now.
Thanks for visiting Adsense Preview - Have a great day!
Regards.