You can choose to add an excerpt when you editing a post, this will be displayed on the blog page. If you haven’t added an excerpt for the post, WordPress will generate one automatically, based on the content. By default, the length of auto-generated excerpt is 55 words. This tutorial shows you how to change that in the theme Customizer.
To change post excerpt length
- Log into your WordPress site administration panel.
- Navigate to Appearance > Customize, choose Blog.
- In the Blog panel, choose General.
- Under Excerpt Length, move the slider to change the number.