For 30 medium russet potatoes (about 13 lbs total), you can bake them all together, but you’ll need to account for the oven being crowded, which slightly extends the cooking time. Here’s what works best:
 
Temperature & Time
Preheat oven to 400°F (200°C).
Scrub potatoes, dry them, and pierce each a few times with a fork.
Place them directly on the oven racks or on a foil-lined baking sheet.
Bake for about 60–75 minutes, depending on size and oven load.
Check after 60 minutes by inserting a fork or skewer—if it slides in easily, they’re done.
If you want extra-crispy skin, rub lightly with oil and sprinkle with salt before baking.
 
Tip for Even Results
Since your oven will be full, rotate the pans halfway through baking.
If baking ahead for service, you can pull them at about 205–210°F internal temperature, then hold in a warm oven (around 180–200°F) wrapped in foil.