Open risk is the number that matters when markets move together. Add up each position's distance-to-stop in dollars, including hedges only when they genuinely offset, and compare the total against a ceiling - commonly 3-6% of equity for active traders.
Example: six positions at 0.75% each is 4.5% of open risk. That is fine on a normal day and is a 4.5% loss on the day everything correlates to 1, which is exactly the day it will happen. Decide in advance whether a 4.5% single-day loss is acceptable; if not, the cap is too high or the positions are too similar.
Open risk falls as stops are raised, which is the mathematical case for moving to breakeven-stop on winners: it frees capacity for new trades without raising the ceiling.
Related: open-trade-risk, portfolio-heat, initial-risk