How many characters can fit in a single standard SMS text message?

How to get close to this number

The answer is an engineering constraint, so expect a number that is round in binary or in bit-budget terms rather than in decimal. SMS was designed to fit inside spare capacity in the mobile signalling channel, and the character count is whatever that budget allowed once a seven-bit alphabet was chosen. Working from "what would fit in a small fixed packet" gets you to the right scale.

The mechanism in the explanation is the interesting part, and most people have experienced it without knowing. Longer messages are not rejected; they are split, with a few characters of each segment consumed by header data so the pieces can be reassembled. That is why a long message occasionally arrives out of order or as several separate texts — the stitching failed rather than the sending.

The character budget also depends on the alphabet. Using any character outside the standard set switches the whole message to a wider encoding and roughly halves the limit, which is why a single accented letter or emoji can silently turn one message into two. The figure quoted is for the standard alphabet, and that qualifier is doing real work.