In the following you can see the particular image dimensions for thumbnails in MH Magazine. In general it’s recommended to always upload images with size of at least 1030 x 438px – this will ensure that WordPress can generate all thumbnails:
- 1030 x 438px (Thumbnails for the MH Slider widget)
- 678 x 381px (Thumbnails for featured images on posts, archives and widgets)
- 678 x 509px (Thumbnails for some custom widgets)
- 326 x 245px (Thumbnails for archives and widgets)
- 80 x 60px (Thumbnails for some custom widgets)
Reading and following these tutorials would be helpful.