Hello

Nowadays when JEE Mains are conducted annually, I believe depending on the toughness of paper in your session, anything above 250 gives you a good chance to secure a Rank in Top 1000 in JEE Main. In 2019, the year I had appeared for JEE Main 300/360 would morw or less ensure one in Top 1000 Ranks, which was almost 83.33 percentage, which roughly converts to 250 in a scale of 300.

Hope this helps