Estimate daily messages sent via SMS + messaging apps

Estimate the total number of personal and business messages sent globally per day across all channels (WhatsApp, WeChat, iMessage, SMS, Telegram, Messenger, Signal).

Context

WhatsApp alone officially reported processing >100 billion messages per day.

Clarifying questions to ask first

Are we counting single outbound sent messages or total received deliveries across group chats? (Outbound messages sent).
Does this include transactional OTPs and marketing SMS? (Yes, all messages).

How to approach it

Deconstruct by Major Platforms: WhatsApp (~140B), WeChat (~60B in China), iMessage / Apple Messages (~40B), Traditional Carrier SMS & RCS (~25B), Others (Telegram, Messenger, Signal, Discord: ~45B)
Bottom-up Demand Validation: Global Smartphone Users (~5.0B) × Average Messages Sent per Day (~60-70 messages/day across all apps)
Account for Group Chat Multipliers (1 sent message delivered to 10 participants)
Synthesize global daily messaging throughput

Framework: Total Global Daily Messages = WhatsApp + WeChat + iMessage + Carrier SMS/RCS + Telegram/Messenger/Others

Sample answer

Platform Breakdown:
- WhatsApp: ~140 Billion/day
- WeChat (China): ~65 Billion/day
- iMessage / Apple: ~40 Billion/day
- Traditional SMS / RCS / A2P: ~25 Billion/day
- Telegram, Messenger, Signal, Instagram DMs, Discord: ~50 Billion/day
Total Outbound Messages = ~320 Billion messages/day

Bottom-up check: 5B smartphone users × 64 messages/day = 320 Billion messages/day (Exact alignment)

Executive estimate: ~300 to 330 Billion messages sent globally every day (~45% on WhatsApp, ~20% WeChat, ~12% iMessage, ~8% SMS).

What interviewers look for

Platform-by-Platform Sizing (WhatsApp/WeChat/iMessage)
Bottom-up Smartphone User Averages
Group Chat Multiplication Factor
Global Volume Aggregation (Hundreds of Billions)