Considering it is for global users across the world
Across mobile platforms (ios and android)
Referring to text messages specifically and not gifs, video or voice calls
Total Messages Sent Per day = Messages sent in Developed world + Developing world + underdeveloped world per day
# of messages sent per day = # of users in every market x average messages sent per user.
World Population 7B, 50% internet penetration → 3.5B
Assuming Whatsapp has 50% penetration in the messaging space → 1.7B users
20% of the world is in developed world, 60% in developing countries, 20% in under developed countries. Assuming the same distribution holds for WhatsApp in these markets
Whatsapp developed user count → 0.2 x 1.7B → 340M users
Whatsapp developed user count → 0.6 x 1.7B → 1B users
Whatsapp developed user count → 0.6 x 1.7B → 340M users
Users in developed countries are reasonable users of WhatsApp but not as strong as developing countries. In general, I would assume 30% of their phone/text conversation happen on whatsapp. Rest happens on iMessage/android SMS, or messenger.
Assuming an average developed country user sends 10 unique messages/day → 3 of them happen on WhatsApp.
Users in developing countries tend to use WhatsApp the most and it accounts for 80% of their conversations. Assuming they send 15 messages per day, 80% of them come on whatsapp → 12 messages.
Users in underdeveloped countries tend to use WhatsApp a lot due to its free nature and it accounts for 80% of their conversations. Assuming they send 5 messages per day, 80% of them come on whatsapp → 4 messages.
Total Messages Sent --> Messages sent in Developed world + Developing world + underdeveloped world per day
→ (340M x 3) + (12x1B) + (340M x 4)
→ 14.4B messages are sent per day on whatsapp