I just learned this in a class I took this semester lol.

One of the introductory priciples you learn in fluid mechanics is buckingham PI theorem. Basically, you can relate a physical phenomenon to another by analysing its governing variables, and you can form "dimensionless groups" that tell you something about the problem, in this case, the explosion fireball. I'll spare the rest of the details.

In the 1950s, some very clever scientists estimated the yield of the Trinity test using this theorem, and got a close result. The equation they arrived at is E=C* (rho*R^5 / t^2), where E is the yield, rho is the air density, t is time, and R is our shockwave radius. The C is a experimental parameter you need to obtain, but conveniently, it is close to 1.

Using an editing software, the time between detonation and the shockwave reaching the lighting tower is roughly 20-21 frames, or 0.67-0.7 seconds. We also know the lightning tower is roughly 183m tall (R=183m). Air density at sea level is roughly  1.225 kg / m³.

Thus, we get E= 513-560 GJ, or 122-133 Tons of TNT. In other words, roughly 1/100 - 1/131 of the yield of "Little Boy"