http://tvtropes.org/pmwiki/pmwiki.php/Main/SlidingScaleOfVillainThreat

An antagonist can be classed on three orthogonal parameters:

This is a method of quantifying the first one.

Superman is locked in a battle with Lex Luthor, who is threatening to melt the polar icecaps and flood the world. Meanwhile, in Gotham , the Joker is going to gas the city. Meanwhile again in space, the Green Lantern is getting ready to defend against the invading Sinestro Corps. All of these examples have villains that are exhibiting differing levels of threat.

You can class various villains on tiers of the type of threat they present to the world and the heroes. The Sorting Algorithm of Evil will usually ensure that the hero's successive opponents will each be higher on the scale than the last, but, due to the SAoE's caring about effectiveness as well as scope, not always. In general, the hero will also have the same potential for destruction as his villains, but usually is slightly below them, because underdogs are more relatable. Having a wild range of villains may help avoid causing a feeling that The World Is Always Doomed because Evil Only Has to Win Once. Having a hero with a Story-Breaker Power usually upsets this dynamic, or forces a jump in villain up the scale.

Advertisement:

Most series that lean towards the realistic side of the scale do not venture beyond villains that are Planetary Threats, as villains that are Stellar Threats and above tends to put a lot of pressure on Willing Suspension of Disbelief. Shifting too far up the scale, especially over a short period of time, is an easy way to Jump the Shark.

When talking about some villains, this is very much related to how much they can abuse the Kardashev Scale for death and maiming. Contrast with Sliding Scale of Antagonist Vileness, when you're talking about the audience's reaction to a character rather than the threat they represent, and Sliding Scale of Villain Effectiveness when talking about how well they succeed.

See also Super Weight, which is more about measuring characters (including villains) in terms of raw power.