One Punch Man: How Powerful Are Boros’s Ship Cannons?

One Punch Man (Anime) Chapter 10

Boros’s ship is not only massive, but also armed with weapons powerful enough to erase an entire city in moments. By analyzing its size and firepower, we can estimate just how destructive its cannons truly are, using physics-based scaling that fits the events shown in the story.

Although there is no official data specifying the exact size of City A, we can still make reasonable estimates without resorting to extreme assumptions, such as each city being the size of an entire country.

To do this, we rely on Genos’s annotations regarding the size of Boros’s ship, shown in Episode 12 of the anime, which provide a solid reference for scaling.

One Punch Man (Anime) Chapter 12

According to Genos’s notes, Boros’s ship measures approximately 9,230 meters × 15,024 meters. (translation of Genos' notes)

To put this into perspective, a city with these dimensions would have an area of approximately 138,671,520 m², or 138 km², meaning Boros’s ship is comparable in size to a major city.

With these dimensions established, we can compare the spaceship to the city below using various manga panels. Only the redrawn versions are considered, since the original panels were discarded by the author.

One Punch Man Chapter 36

From this comparison, the city’s radius measures about 655 units, while the ship measures 130 units. This makes the city roughly 5 times wider than the ship. Translating this to real values gives a city radius of approximately 75,120 meters, resulting in an area of about 17,728,052,583 m², or 17,728 km².

For comparison, City A would be about 1.31 times larger than the Greater Tokyo Metropolitan Area, including its prefectures (13,452 km²). This should be considered a minimum estimate, since no single image shows the entire city, but it provides a reasonable working scale.

Cannon Power

To devastate an area of this size, collapsing all reinforced concrete buildings, we must consider blast overpressure. A pressure of 20 psi is typically required to destroy concrete structures.

For this, we apply the Glasstone & Dolan / Kingery–Bulmash airblast model, using the following relation:

$$Y = \left(\frac{x}{0.28}\right)^3$$

Where:

• Y = explosive yield in kilotons of TNT

• x = blast radius in kilometers

• 0.28 = empirical constant corresponding to 20 psi overpressure

Substituting our values:

$$Y = \left(\frac{75.12}{0.28}\right)^3 \approx 19{,}310{,}461\ \text{kilotons of TNT}$$

This corresponds to approximately 19,310 megatons of TNT, placing the ship’s cannons firmly in the extreme city-destruction range, consistent with the scale shown in the story.

One Punch Man Chapter 32

Now, how powerful would each projectile be?

Based on the attack sequence, it is possible to count roughly 70 points of light on one side of the ship, which can reasonably be interpreted as individual cannons. This implies a total of about 140 cannons.

Dividing the total yield by this number, each projectile would carry approximately 137 megatons of TNT in kinetic energy.

These points of light are indeed cannons, as shown later in the chapter, where each light emits a single projectile, confirming that the ship fires discrete shots rather than a continuous beam.

One Punch Man Chapter 32

Even as a minimum estimate, the level of power demonstrated by Boros’s ship is astronomical. Each individual projectile reaches energy levels comparable to the meteor that threatened to destroy City Z, highlighting just how overwhelming the ship’s firepower truly is and reinforcing Boros’s status as an extreme planetary-level threat.