Estimate handwriting speed in words per minute.
Handwriting speed is words divided by minutes, measured over a sample long enough to be representative — at least five minutes of continuous writing, since a one-minute burst overstates what you can sustain. Adults typically write 20 to 30 words a minute legibly. The exam projection applies a 0.8 factor to the measured rate because hand fatigue and thinking time reduce sustained output over a long paper, and the page figure assumes about 250 handwritten words to a side.
Writing speed
Words per minute = words written / minutes taken
Exam output
Exam words = wpm x exam minutes x 0.8 sustained factor
Around 20 words a minute legibly covers most timed essay papers, since perhaps two thirds of the time goes on thinking and planning rather than writing. Below about 15 wpm, timing becomes the binding constraint.
Past your comfortable rate, yes, and illegible answers cannot be credited. Practising at a sustainable speed beats pushing the ceiling, because the marker's reading rate is what ultimately matters.