If comparing the main theme park footprints, Universal Studios Hollywood is significantly larger than Disney California Adventure. Universal Studios Hollywood spans about 415 acres, but much of that is the "Backlot" used for actual film and TV production. The actual guest-accessible theme park area is smaller. In contrast, Disney California Adventure is approximately 72 acres. However, if you look at the total "resort" footprint, the Disneyland Resort (which includes Disneyland Park, California Adventure, and Downtown Disney) covers about 486 acres. While Universal has a massive total acreage due to its working studio, the "walkable" theme park space in Disney California Adventure feels more dense. If you are asking about Orlando, the comparison flips: Walt Disney World (25,000 acres) is nearly ten times the size of the entire Universal Orlando Resort (approx. 540 acres, expanding to over 1,300 with Epic Universe).