EBITDA Margin is the ratio of EBITDA to Sales Revenue. Example: Revenue of $10,458 and EBITDA of $871 yeilds EBITDA Margin of 8.3%.

EBITDA Margin = EBITDA/Sales

Yes, EBITDA Margin can be negative. When a company is positive it is due to good efficiencies processes that have kept certain expenses low. While Negative EBITDA can suggest the contrary.

Depends on what you're comparing it to. Since EBITDA is a dollar amount, it's not really something you can compare between companies, especially of different sizes. Obviously, you want EBITDA to be positive, as it is essentially revenue. It would help with comparisons to convert it to a percentage change. (EBITDA2 - EBITDA1)/(EBITDA1) where EBITDA2 is EBITDA at period 2 and EBITDA1 is EBITDA at period 1. That way, you can see how much EBITDA has grown for a given company in a percentage. Then, you can compare it to similar companies. Higher is usually better.

Not necessarily. A negative EBITDA implies that the entity is not capable to cover its interest and tax payments with its operating profits.