So in Volume 7 & 8 Megumin had pointed up and done an explosion in the air. It caused all the windows within town to shatter. Using the calculated diameter here , this is pretty straight forward, i'm just looking for the 1 psi range.

Feat[]

Since Axel is  6,976.8 meters in diameter and the feat was an airburst, using nukemap:

• Height of burst = 740 Meters
• Yield = 4 Kilotons
• 1 PSI Diameter  = 6.8 KM

The height of burst can also be set to anything between 450 and 740 meters to get the around the same 1 psi range, just that within those you get the 20 psi range too so I just went high enough to make it disappear. 

Yes the range doesn't match the given diameter but the given yield wouldn't nudge past that range so simply changing the yield to 5 kilotons will give a 7.26 km in diamater 1 psi range (below)

Results[]

4/2 = 2 Kilotons

5/2 = 2.5 Kilotons