Discord's Size[]
Finding Some kind of Standard[]
PONY.MOV is kind infamous for size and shape being wonky, but at this point I'll take what I can get.
In SPIKE.MOV we can se a size comparison of Spike and Paco, if we assume Paco is 12 years old, we can assume he's around 54 inches tall, and since it's implied that he's on this tippy toes to better see Spike's techdeck, they should at least be similar height.
Time to compare Spike and Twilight before getting to the actual calculation
718 pixel tall spike
1021 pixel tall twilight
54 / 718 = 0.075 inches per pixel
1021 x 0.075 = 76.575 inches tall
We can convert inches into meters: 1.94 meters
Now we're going to have to use Angular Size to compare Spike and Wolfmother (Who is the same size as Discord)
Angle Sizing[]
1080 pixel tall cam
55 pixel tall twilight
986 pixel tall Wolfmother
2atan(tan(35deg) x (object size in pixels/panel height in pixels)) = 2atan(tan(35deg) x (55/1080)) = 4.08 degrees
Using the calculator to solve for distance, we get 772.04 pixel distance
Using Wolfmother's pixels we use this:
2*tan(70deg/2) * 772.04 * 986 / 1080 = 987.07 pixels
(Twilight's estimated height) 1.94 / (Twilight's Pixel Height) 55 = 0.035 meters per pixel
987.07 x 0.035 = 34.54 meters tall
With Wolfmother having a very humanoid form besides his legs, I feel like we can use the standard male... so Wolfmother, and by proxy, both Discord and Rainbow Dash (Giant Form) should be Small Building level via sheer size and from fighting the other.
Discord's fireball explosion[]
Finding Some kind of Standard[]
Since we don't really get a shot of anyone on screen, I'm going to have to use the good old assumption of standardized door size, which is 80 inches, or 2.03 meters.
1080 pixel tall cam
122 pixel Door height
853 pixel explosion diameter
2atan(tan(35deg) x (object size in pixels/panel height in pixels)) = 2atan(tan(35deg) x (122/1080)) = 9.045 degrees
Using the calculator to solve for distance, we get 771.21 pixel distance
Using the explosion's pixel's:
2*tan(70deg/2) * 771.21 * 853 / 1080 = 853.01 pixels
(Door's estimated height) 2.03 / (Door's Pixel Height) 122 = 0.016 meters per pixel
853.01 x 0.016 = 13.64 meter diameter, or a radius of 6.82 meters. Small Building level.