Reaper use those markers along the right side of the pic to indicate size. I cant remember if the space is 1 inch or a half but im sure you can find out on their site.
Not to sound too rude (OK, perhaps just a little!) but did you even try typing "reaper minotaur" into a search engine Even without adding "scale" or "size" it brings up plenty of comparisons.
Since it's available in "bones", it's a pretty common and commonly photographed model, and was among the first "wow, what size are these?" models when their Kickstarter was going on.
*Edit* It occurs to me that this is one of the few Ogre-sized models I didn't buy in "bones" form. Are you looking at getting the metal or bones/plastic version? I found the larger models came out better than the smaller ones when made in this material. For the sake of a couple of dollars you can't go too wrong, I guess
Also - will def get the metal as this will get massively converted and I need the model to have a bit of resilience.
Also not too fussed on the Bones Plastic tbh. Call me a snob but I'm a bit of a metal puritan when it comes to jobbies like this.