It’s very simple to resize your post area in Blogger and it works in most of the Blogger templates. Here’s how to do it in 4 quick steps.
Open Blogger Template Designer
Open your Blogger dashboard and go to Template page. Then, click on the Customize button.
Open Adjust Widths from the menu
Once inside, choose Adjust Widths from the menu on the left side.
Use the slider to find your desirable width
The next part is when you actually decide how you want your blog to look like. Use the available sliders to find the width you want and see the results in real time.
Keep in mind that the number displayed in the entire blog field is really the entire blog’s width so your post area is smaller than that. Usually it’s the entire blog width minus the sidebar width and minus some margins in between.
If it’s the sidebar width that you want to change, use the appropriate slider, but notice that widening the sidebar automatically changes the post area width. So if you only want to make the sidebar wider, you need to increase both the sidebar and the entire blog value.
OK, that’s it! Just click the Apply to Blog button and you’re done.