how much dxm is too much

just wanna know how much of dxm could be potentially lethal, assuming you 'do' nauseate and throw up. i wanna do it again but im lowkey scared cus i think ive gotten my tolerance pretty high up (500mg) really soon, like maybe only after two trips and i dont wanna die trying it the next time so id really appreciate it if you folks could help me out selecting a dose i shouldn't surpass (18F, 92lbs)