Image size guide
Shopify allows you to upload images up to
5760 x 5760px with a file size of up to 20 MB, but generally recommends using images around
2048px wide which should cater for the majority of devices.
Most common screen sizes
According to W3schools 1366px wide x 768px high is the most popular screen resolution as of January 2018 (not including mobile devices).
For images in your store, if you use
2048px for full width images, an easy rule of thumb is to divide that by number of vertical columns on the page.
2048px for full width images
1536px for three-quarter width images
1024px for half width images
768px for quarter width images
Shopify recommends using product images with dimensions up to
2048 x 2048px.
These are high resolution images with great zoom capabilities. Keep in mind that for zoom functionality to work, your images have to be larger than
800 x 800px.
Slideshow images will adjust their height based on the dimensions of the image uploaded. If you'd like it smaller, adjust the height before uploading, for example
2048 x 500px.
Consistency is key!
To make your images look the same side by side, you need to use a consistent aspect ratio, or height-to-width ratio, for all the images that you add as your featured image.
For more info read Shopify's guide on image aspect ratios.