The number people quote is around 200 to 250 words per minute for adult reading. That is roughly right for English and roughly wrong for most other languages.
Standardised reading-rate measurements across seventeen languages put average silent reading at approximately 228 words per minute in English, 218 in Spanish, 202 in Dutch, 161 in Finnish, 158 in Chinese and 138 in Arabic.
Most of that spread is not about readers. It is about words. Languages differ in how much meaning they pack into a word, so counting words compares different amounts of content. Measured in characters per minute the gap narrows considerably — the seventeen-language average lands around 863 characters per minute.
The practical consequence: an app with one global default speed is mis-set in most languages by construction. 300 words per minute is demanding in Arabic and slow in some others.
Reading rate alone is easy to inflate — you can move your eyes across a page as fast as you like. The number that matters is the rate at which you still understand.
With single-word presentation, comprehension is comparable to normal reading at 250, 300 and 350 words per minute, and drops measurably at 400 and 450. Above 500 it degrades for everyone, and more sharply when reading in a second language. So the honest ceiling for most people, most of the time, is somewhere just under 400.
This deserves its own line because it is consistently underestimated. The drop at high speed is steeper for non-native readers. If you are reading in a language you learned later, your comfortable rate is lower — not because you read badly, but because recognition is doing more work per word.
Punctum sets a different starting speed per language for exactly this reason. More in does speed reading hurt comprehension.