Approximately how thick is the cerebral cortex?

• A. 1-2 mm
• B. 2-6 mm
• C. 6-12 mm
• D. 12-20 mm

Answer: (B)

The cortex is a very thin sheet of gray matter that covers the outer surface of the brain. In adults, its thickness is typically a few millimeters—about 2 to 4 mm on average—with regional variation that can push some areas toward thicker values. Different measurement methods (histology vs MRI) can yield slightly higher numbers, often cited up to around 5–6 mm in places. So the broad, approximate thickness is 2–6 mm. A 1–2 mm estimate is generally too thin for most cortex, while 6–12 mm or 12–20 mm would be far thicker than the cortex actually is.