How far is it to the center of the Earth?

• A. about 3,000 mi
• B. about 5,000 mi
• C. about 4,000 mi
• D. about 6,000 mi

Answer: (C)

The distance to the center is the Earth's radius. The Earth’s average radius is about 3,959 miles (6,371 kilometers), so rounding gives about 4,000 miles. A quick check comes from the circumference: roughly 24,900 miles around the equator, and radius is circumference divided by 2π, which is about 3,960 miles. The planet isn’t a perfect sphere, but this four-thousand-mile figure is the close, practical estimate. The diameter would be about 8,000 miles.