In order to understand text messages, it is helpful to use the "shipping container" analogy to describe how data travels across mobile networks.
1. Think of Every Text as a Shipping Container
Think of a single SMS as a standard-sized shipping container.
The Fixed Size: Just as a container has a set volume, the global cellular network was built to carry data in small "packets" of exactly 140 bytes.
The Packing List: In the 1980s, engineers realized they could fit exactly 160 basic characters (letters and numbers) into one of these 140-byte containers. This became the international "standard size" for one text message.
2. Emojis Use "Heavier" Items
If you add an emoji or a special symbol (like a non-English character), it’s like trying to ship a heavy grand piano instead of a cardboard box.
More Space Required: These "complex" characters take up much more digital space (bits) than a simple letter.
The Result: Because the shipping container size never changes, you can only fit about 70 of these "heavy" characters into a single message instead of 160.
3. Long Messages Require Multiple Containers
When you write a text longer than 160 characters, your software doesn't just "stretch" the container; it has to use multiple containers (called segments).
The "Assembly" Fee: To make sure the phone on the other end knows how to put the pieces back together in the right order, a small amount of space in each container is used for "shipping labels" (hidden instructions).
Reduced Capacity: Because of those labels, your second and third containers can only hold about 153 characters each instead of the full 160.
Summary for the Customer:
160 characters is the universal "one-unit" limit for plain text.
70 characters is the limit if you use emojis or special symbols.