The original calc[]
The first calc I've made here, hope you like it.
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Here I'll calc about Base Mettaton Physical power.
Frisk's heigh is 91 px.
I assume Frisk's age is from 8 to 12
https://www.disabled-world.com/calculators-charts/height-weight-teens.php
Here are averare heighs based of children's age and since Frisk's gender is unknown, I'll use heighs of both genders.
So we have: Female Children : 128.2 cm (8 yrs), 133.3 cm (9 yrs), 138.4 cm (10 yrs), 144 cm (11 yrs), 149.8 cm (12 yrs)
Male Children: 128 cm (8 yrs), 133.3 cm (9 yrs), 138.4 cm (10 yrs), 143.5 cm (11 yrs), 149.1 cm (12 yrs)
I'll make the arithmetic average's heigh so Frisk' heigh= (128,2 + 133,3 + 138,4 + 144 + 149,8 + 128 + 133,3 + 138,4 + 143,5 + 149,1)/10 = 138, 96 cm
Here MTT creates a hole in the wall with his mere physycal streigh
Now let's go to the image:
Red line = Frisk's heigh = 91 px = 138, 96 cm
Blue line = Hole's width = 176 px = 268, 76 cm
Orange line= Hole's height = 184 cm = 280,97 cm
The hole's area = 268,76 cm * 280,97 cm = 75513,4972 cm^2
Now for the volume we need the hole's thickness
An average wall's thickness is 4,5 inches and 4,5 inches = 11,43 cm
Hole's volume= 75513,4972 cm^2 * 11,43 cm = 863119.273 cm^3
I guess the wall was pulverized since there's only the hole but not the wall's pieces
Pulverization's energy is of 214.35 j/cc
So the energy is 863119.273 cm^3 * 214,35 = 185009616,16755 joules = 0.04422 Tons = 44,22 Kilograms of TNT (Small Building level)
This is an upgrade since I think this feat is better than Undyne's
AlexSoloVaAlFuturo's correction[]
Alex made me notice that the hole Mettaton created isn't a perfect quare, but is smaller, so I'll make again the calc for know how big is exactly that hole
In the new image, Frisk's heigh is 92 px, and his heigh in cm is the same of the previous calc, same with the thickness (11,43 cm)
92 px = 138, 96 cm
The Purple square is the area of all the hole, including also what wasn't damaged
The purple square's sides are all of 186 px = 280.94 cm
The purple square area is (186 px)^2 = (280.94 cm)^2 = 78927,2836 cm^2
Now let's see the area of what wasn't damaged
Blue Triangle's area = 40 px * 31 px = (60,41 cm * 46,82 cm)/2 = 2828,3962 cm^2 / 2 = 1414,1981 cm^2
Water Blue Rectangle's area = 38 px * 31 px = 57,40 cm * 46,82 cm = 2687,468 cm^2
Orange Rectangle's area = 109 px * 31 px = 164,64 cm * 46,82 cm = 7708,4448 cm^2
Grey Triangle's area = (51 px * 66 px)/2 = (77,03 cm * 99,69 cm)/2 = 7679,1207 cm^2 / 2 = 3839,56035 cm^2
Pink Triangle's area = (54 px * 83 px)/2 = (81,56 cm * 125,37 cm)/2 = 10225.1772 cm^2 / 2 = 5112.5886 cm^2
Green Triangle's area = (26 px * 20 px)/2 = (39,27 cm * 30,21 cm)/2 = 1186,3467 cm^2 / 2 = 593,17335 cm^2
Light Green Triangle's area = (22 px * 15 px)/2 = (33,23 cm * 22,66 cm)/2 = 752,9918 cm^2 / 2 = 376,4959 cm^2
Brown Triangle's area = (20 px * 29 px)/2 = (30,21 cm * 43,80 cm)/2 = 1323,198 cm^2 / 2 = 661,599 cm^2
Brick Red Triangle's area = (23 px * 20 px)/2 = (34,74 cm * 30,21 cm)/2 = 1049,4954 cm^2 / 2 = 524,7477 cm^2
Olive Green Rectangle's area = 14 px * 29 px = 21,15 cm * 43,80 cm = 926,37 cm^2
The hole's area = 78927,2836 cm^2 - ( 1414,1981 cm^2 + 2687,468 cm^2 + 3839,56035 cm^2 + 5112,5886 cm^2 + 593,17335 cm^2 + 376,4959 cm^2 + 661,599 cm^2 + 524,7477 cm^2 + 926,37 cm^2 ) = 78927,2836 cm^2 - 16136,201 cm^2 = 62791,0826 cm^2
Hole's volume = 62791,0826 cm^2 * 11,43 cm = 717702,074118 cm^3
The pulverization of the steel is the one which was suggested, so I'll use it
Low End = 717702,074118 cm^3 * 310 j/cc = 222487642,977 Joule = 0,053 Tons = Small Building Level
Mid End = 717702,074118 cm^3* 655 j/cc = 470094858,547 Joule = 0,112 Tons = Small Building Level
High End = 717702,074118 cm^3 * 1000 j/cc = 717702074,118 Joule = 0,172 Tons = Small Building Level