Small Intestine Length: Anatomy and Measurement

The adult human small intestine measures approximately 6 meters (20 feet) from the pyloric sphincter to the ileocecal valve.

Regional Lengths (Variable)

• Duodenum: ~25 cm (10 in) — fixed, retroperitoneal.
• Jejunum: ~2.5 m (8 ft) — proximal 2/5; larger diameter, thicker wall, prominent plicae circulares.
• Ileum: ~3.5 m (12 ft) — distal 3/5; smaller diameter, thinner wall, Peyer's patches.

Measurement Notes

• Cadaver/autopsy: Longer (no tone) — up to 7–8 m.
• Living (surgery/endoscopy): Shorter due to smooth muscle tone.
• Functional length amplified by plicae circulares (×3), villi (×10), microvilli (×20) → total mucosal surface ~250–300 m².

Clinical Relevance

• Short bowel syndrome: <200 cm (adult) → malabsorption.
• Resection limits: Preserve ileocecal valve and >100 cm jejunum+ileum if possible.
• Capsule endoscopy traverses entire length.

Length varies by height, age, and measurement state. 6 m is the standard living-adult estimate.