Simple Themes - Recommended Image Sizes
Featured image size
For your featured images, we recommend your images be at least 800x1100px, but no larger than 2400x2400px. This size will ensure your images display correctly in all areas of your site: front page, category pages, etc. Your images don't need to be any particular size or shape, as long as both dimensions (width and height) fall between this size range.
Note about max image size
WordPress has a limit to how large your images can be. This limit is 2400px (either width or height) and is set by WordPress, not your theme. If you attempt to upload images larger than this, one of two things may happen: the image may not upload at all and produce an error; or, the image may upload but the thumbnails (AKA the image sizes used in your theme) will not be able to generate for the image. This can cause the image to display incorrectly in your theme. Correctly sized images are very important!
Image sizes inside blog posts
The width of the blog post column is 700px. For the clearest possible display, we recommend uploading images roughly twice that size (1400px is great).
If page speed is a concern, then you can upload images right at 700px. Larger images really won't affect your page speed all that much, unless you have a huge number of images in one post.
If you're using the full width post layout, the post column is 950px and images should be at least that size.
Blog post slider
If you are using one of the Post Slider homepage options for your theme ( example), your featured images will need to be a bit larger.
- Content width slider: Minimum for the slider: 1060x600px; OPTIMAL minimum: 1060x1100px (to meet featured image height requirement above).
- Full width slider: Minimum for the slider: 1600x700px; OPTIMAL minimum: 1600x1100px (to meet featured image height requirement above).