>>95967676
It's kind of a difficult question to answer really.
Folklore speaking Goblins are mostly pretty diminutive as far as I'm aware. They operate in the same sort of mythical basis as Faeries, Gnomes, Hobs, and all of the various other small spiritual tricksters and helpers.

Tolkien helped codify the Goblin as a fantasy staple alongside later works it influenced (D&D and Warhammer mostly)
Notable though is that Tolkien is the creator of the word Orc which in his stories were simply another name for Goblins. But due to his varying descriptions and interchangeable use of the words they slowly metastasized into distinct creatures.

D&D made them distinct, but also introduced other sub-types of goblins like Hobgoblins and Bugbears. Based on various legends and myths so now we've got Goblins, Orcs that aren't goblins, large militaristic Goblins reminiscent of Tolkien's Orcs/Goblins, and finally bugbears that without looking into I have no idea of their origin off the top of my head.

Warhammer shows up as well and becomes the basis of essentially the standard modern fantasy Goblin and also conveniently (or not) ties them back to Orcs again. Bright green skin comes from Warhammer as far as I'm aware. Here they're presented as related to Orcs but still slightly distinct. Mostly by size but there are still large Goblins that are Goblins not Orcs.

So I guess the answer to your question would be anywhere from about a foot tall to about seven feet tall. Depending on your source of inspiration and opinions on what a "proper" goblin is.

Pic (probably) unrelated. It's a matter of perspective.