How much g force kills you?

Sustained g-forces above 10-15g are typically fatal for unprotected humans, though the exact lethal threshold depends on direction, duration, and individual physiology. Horizontal g-forces (front-to-back) are more tolerable than vertical forces (head-to-toe), which disrupt blood flow to the brain. As little as 4-5g sustained for more than a few seconds can cause blackouts in untrained people, potentially leading to fatal conseuences if operating vehicles or aircraft.