Open Gmail
Click the checkbox at the top left to select all visible emails
Click the “Select all conversations in Inbox” link if it appears
Click the “Mark as read” icon in the toolbar
To mark all mail in a label as read, open the label first and repeat the same steps
To mark all Gmail messages as read, use the search bar and search for `is:unread`
Select all results
Click the “Mark as read” icon
On mobile, open the Gmail app
Tap the sender photo or press and hold an email to select it
Select multiple emails
Tap the three-dot menu
Tap “Mark as read”