Check marks will appear next to each message you send. Here's what each one indicates:
In a group chat, the second check mark appears when all participants in the group have received your message. Two blue check marks appear when all participants in the group have read your message.
For any message that you send, you'll be able to see a message info screen, displaying the details of when your message was delivered, read, or played by the recipient.
To see the message info screen:
The message info screen shows:
Read or Seen:
Note: When a participant leaves a group, the Message info screen will still show the original information with all participants, including the participant who left the group.
If you don't see two blue check marks next to your sent message:
To turn off your read receipts, tap More options > Settings > Account > Privacy and turn off Read receipts.
Note: This won't disable the read receipts for group chats or play receipts for voice messages. There's no way to turn those settings off.