When it comes to photos for a WordPress blog, usually the size of the photo doesn’t really matter. However, there are times when you may want to make sure your photos are sized correctly for the blog layout.
Generally speaking, WordPress will automatically resize a photo to fit the size of the blog post it’s placed in, but sometimes you may want to resize a photo yourself in order to make sure it looks good on all devices.
Generally speaking, WordPress suggests that photos be no larger than 800 pixels wide by 600 pixels high. However, this is just a general guideline – you should always test a photo before uploading it to see how it looks on your blog.
Additionally, if you’re using a theme or plugin that includes custom media galleries or galleries within posts, be sure to check the size restrictions associated with those galleries as well.