Well you can actually make it a pattern in Photoshop.
With the tile open, select all and choose
Edit > Define Pattern. Then it's a pattern just like all the other built in Photoshop patterns.
If you know the tile size you can create a new document the size of 4 tiles, then just apply a pattern fill layer.
With a 500x500px tile, create a 1000x1000px document and choose
Layer > New Fill Layer > Pattern... selecting your pattern.
If you don't know the tile size, and it's already a pattern in Photoshop... You can turn on Tool Tips in the Preferences, then hover your mouse over a pattern and the tip will show you the tile size: