@Brony2893  
You should check out her art some time.

@QueenCold  
You… I like you

@dragonSpike
 
Ponies may have been described as hip-high on discussion boards, but never in canon.  
The only time in the show we were told the actual size of something was in the hearth’s warming eve episode, when Twilight spotted an 8 ft. candy cane. This candy cane was about 3 times as tall as Scootaloo.  

 
8/3≈2.67
 
 
 
(don’t mind the caption)
 
Although Spike’s size is a bit inconsistent throughout the episodes, he is always about the size of a filly, so he’s roughly between 2’6” and 2’8”, not counting his head spines.
 

 
A human would have to be freakishly large to even have knees 2 ft above the ground.  
In other words, Spike is clearly taller than just knee high.
 
But even if he were knee high, he’d still be depicted too small in this image.
 
 
Analyzing is fun!

@QueenCold  
Ponies have been described as hip-high, he looks to be about knee high in this which would fit his size to ponies.

Heh. He is much bigger than that.

He’s gonna be expensive to feed.

I didn’t think you could keep a.dog in a terrarium… which I not doubt spelled wrong but am to lazy to find the right spelling for.

His teeth can crush gems and he has firebreath. Something tells me a glass tank with a wooden finish isnt gonna hold him for long.

best pet