When developing a site you must check that your site works properly at different screen sizes. I have included 640x480 just in case you are developing your site for that screen size. Most sites are designed to work on a minimum screen size of 800x600.
The main thing to note is that the length of a page is not as important as the width. If your page is too wide then you will force horizontal scrolling which should be avoided at all costs. However you must make sure you get your message across BEFORE the user has to scroll down.
Current stats show 95% of surfers are browsing using a screen resolution of 800x600 or bigger which means that if you develop your site to work on 800x600 your site will work OK for the majority of visitors.
There are arguments against fixing page width but decisions have to be taken and if you want your site to be viewed at its best by the majority of visitors then fix the width.
Using the form below - enter your homepage address then click on the screen size you want to test.
A new window will open at the correct size and your site will display in that window. Make changes to your page until there is no horizontal scrolling. Once your page works you should do a final test by changing your screen resolution properties as there are slight differences that occur between resolutions that could possibly force horizontal scrolling.Only use this window test as a development aid and always validate your page completely by changing your screen resolution properties.