How much stress is bad for you?

Stress: If it interferes with your ability to focus or perform your activities of daily living or start losing interest in activities you normally enjoy.

It depends on: How it affects our functioning or performance. We tend to perform at our peak with just the right amount of stress. Too little and we are insufficiently motivated. Too much and our performance deteriorates. Chronic stress can accumulate and result in what is often called burnout. I think the only measure of stress is a functional one.