Depends on if you want them to browse for their food when it's available or if you are willing to feed them on a "dry lot" or mostly dry lot. If you need them to forage for food, then I'm not quite sure the requirements but I would definitely supplement as the pasture/brush goes down. It's good to give them hay before turning out anyways, to prevent runny poop.
If you plan on feeding them free-choice hay then for two goats, I'd say maybe about 40x40 feet w/ toys to play on to keep them busy. That's just my personal opinion, not really from an expert.
What I have for 6 mini does is an approximate 60x40 pen with an attached 8x12 shed, they have toys to keep them occupied. I do feed them hay year round, more so in the fall and winter, they do have an acre to browse on though, unfenced so they are supervised when out of the pen.
Rule of thumb is eight goats an acer if no feed etc., living off the land. However, with feed/hay you can do much more on that. Shelter is your main issue and the parisites. The more goats you get per acer, the more the parisites will become an issue if there it too much over crouding even with correct hay, feed and shelter.