A single gram of uranium could feed all of humanity for roughly 800 days (2.192 calendar years). Some factors that we're gonna standardize for simplicity:
Everyone eats exactly 2,000 calories
The world's population stays at exactly 8 billion
8,000,000,000 • 2,000 = 16,000,000,000,000
16,000,000,000,000 ÷ 20,000,000,000 = 800