Lucas from Magoosh assures that there is no maximum. You can write an enormous essay and get a perfect score. Official recommendations from ETS, the company that makes the TOEFL, gives specific numbers for essay length in all their preparation material and during the actual test. The recommendations are simple: Integrated essay: 150 - 225 words Independent essay: 300 words.
Check out: How Long to Study for TOEFL or IELTS
These aren’t maximum scores, nor are they minimums. But to be honest, an essay that’s shorter than these recommended lengths may not get a perfect score. Usually, top scoring essays are longer. Still, writing much more does not mean a higher score.
Quantity and quality
There’s a clear reason why shorter essays might have lower scores—they don’t have enough room to include details. That means the essay is not just shorter, but also lower quality. A longer essay gives enough room to add those important details.
Still, a long essay can cause a problem. Imagine trying to write 1,000 words in 30 minutes for the independent essay. How much will you be able to focus on grammar, vocabulary, structure, and clarity? Not much. The more you write, the less attention you can pay to each word and sentence. In other words, it’s possible to write too much, but only because you’re not focusing on the more important aspects of your essay. It’s possible to write a 1,000 word essay and get a perfect score, but Lucas doesn’t recommend trying it.
Check out: A 7-step Plan for the TOEFL Integrated Essay
Reach the recommended length
It’s much easier to write a 400 or 500 word essay with a perfect score. So first, try to reach the recommended lengths from ETS. If you can write more, that’s best. But don’t worry about writing two times the recommended length—it’s better to focus on quality at that point, not quantity.