One-Punch Man: How Destructive Was the Dragon-Level Meteor?

One Punch Man Episode 7

The meteor is the first Dragon-level threat introduced in the manga, with the power to wipe out City Z. But how powerful would its impact actually be?

To estimate the energy of the collision, we use the kinetic energy carried by the meteor. This requires determining two variables: its mass and its velocity.

The manga does not provide direct data for either value. However, it does offer visual and narrative clues that allow us to make reasonable estimates. In addition, we can rely on the official guide One-Punch Man: Hero Encyclopedia, written by the manga’s own author. This guide states that the meteor has a diameter of 200 meters and is classified as a Dragon-level threat, giving us a solid foundation for the calculation.

One-Punch Man: Hero Encyclopedia

The meteor’s shape varies slightly depending on the source. In the webcomic, it appears spherical, with an approximate volume of 4,188,790 m³.
In the manga, however, it has a more ellipsoidal shape.

One Punch Man Manga Chapter 21

By comparing proportions in the manga image (about 647 px in length and 450 px in width), we get a difference of roughly 30%. Using a length of 200 m and a width of 140 m, the ellipsoid volume is:

$$V = \tfrac{4}{3}\pi abc = \tfrac{4}{3}\pi (100)(70)(70) \approx 2{,}052{,}510\ \text{m}^3$$

The meteor’s material is most likely an iron–nickel alloy. It does not fragment under Metal Knight’s missiles, does not melt from Genos’s blast, and survives atmospheric reentry temperatures of around 3,000 °C. With a density of 7,850 kg/m³, the meteor’s mass is:

$$M \approx 1.61 \times 10^{10}\ \text{kg}$$

The minimum speed for an object captured by Earth’s gravity is 11.2 km/s. Using this value, the kinetic energy is:

$$KE = \tfrac{1}{2} M v^2 \approx 1.0 \times 10^{18}\ \text{joules}$$

This is equivalent to about 241 megatons of TNT.

For the webcomic version, the mass increases to 3.29 × 10¹⁰ kg, giving an impact energy of approximately 2.0 × 10¹⁸ joules, or 478 megatons of TNT.

These values make Genos’ concern that the meteor would destroy City Z and its neighboring areas entirely reasonable—the impact energy would have been catastrophic on a regional scale.

Even using conservative assumptions, the meteor’s impact reaches hundreds of megatons of TNT, easily justifying its Dragon-level threat status. Its potential to erase City Z and devastate surrounding areas is fully consistent with the physics-based estimates and the manga’s narrative.