How big is a square in D&D 4e?

I'm curious to know, just how big is a square in Dungeons & Dragons 4th Edition? I've been playing for a while, but I've never quite been able to grasp the exact dimensions of the grid. Is it a standard size that's used across all maps, or does it vary depending on the specific game or scenario? And if it's a standard size, what are those dimensions? I'd love to have a clearer understanding of the scale of the game world as I'm navigating through it.