A standard upper endoscopy reaches about 60 centimeters (roughly 2 feet) past your teeth, ending at the first section of your small intestine. A colonoscopy travels considerably farther, covering the full length of your large intestine, typically 150 to 170 centimeters. These are the two most common types, but specialized scopes and swallowable cameras can go even deeper.
How Far an Upper Endoscopy Reaches
An upper endoscopy (also called an EGD) follows the path food takes after you swallow. The scope passes through your esophagus, into your stomach, and ends at the duodenum, which is the first curve of your small intestine. The scope itself has a working length of about 100 to 110 centimeters, but it only needs roughly 60 centimeters of that to reach the duodenum in most adults. The rest gives the doctor slack to maneuver and get better views of the lining along the way.
This means an upper endoscopy covers three organs but stops well short of the deeper small intestine. If your doctor needs to see beyond the duodenum, they’ll use a different tool.
How Far a Colonoscopy Reaches
A colonoscope is longer, typically 160 to 170 centimeters in working length, and enters from the other direction. It travels through the rectum, up through the sigmoid colon, around the bends of the transverse colon, and ideally all the way to the cecum, which is the pouch where the large intestine begins near your appendix. In most people, the distance from rectum to cecum is around 150 to 170 centimeters, though it varies significantly from person to person.
Reaching the cecum is considered the benchmark for a complete colonoscopy. Current quality standards from the American Society for Gastrointestinal Endoscopy require doctors to reach the cecum in at least 95% of patients with intact colons. The median time to get there is about 9 minutes, though it can take longer depending on anatomy.
Why Some Colonoscopies Fall Short
Not every colonoscopy makes it to the end. The most common obstacles are a colon that’s longer or more twisted than average, looping of the scope, sharp bends that are hard to navigate, and advanced diverticular disease (small pouches in the colon wall that can distort its shape). Prior abdominal surgery can create adhesions that fix parts of the colon in place, making it harder for the scope to advance.
Anatomy plays a measurable role. People whose colon measures 200 centimeters or longer from rectum to cecum are significantly more likely to have an incomplete procedure. The number of sharp-angle bends matters too. People with 10 or more acute flexures in their colon are at higher risk of an incomplete exam. Women, older adults, and those with diverticular disease are statistically more likely to fall into these categories. When a colonoscopy can’t reach the cecum, doctors typically recommend a CT colonography (virtual colonoscopy) to visualize the remaining portion.
Reaching the Small Intestine
The small intestine is the hardest part of the digestive tract to examine with a scope. It’s roughly 6 meters (20 feet) long and folded into tight loops, making it too deep for a standard upper endoscopy and inaccessible from the other end by colonoscopy. Specialized techniques exist to get further in, though none are as routine as an EGD or colonoscopy.
Push enteroscopy uses a longer, stiffer scope inserted through the mouth. It can reach 40 to 120 centimeters past the stomach, which covers a meaningful portion of the upper small intestine but still leaves most of it unseen.
Balloon-assisted enteroscopy goes much further. These scopes use one or two inflatable balloons to grip the intestinal wall and accordion the bowel over the scope, letting it inch forward through loops that would otherwise push it back. Using both an oral and rectal approach in combination, double-balloon enteroscopy can visualize the entire small intestine in 40% to 80% of cases. Single-balloon enteroscopy can achieve similar results, though data is still accumulating on its total reach.
Capsule Endoscopy: Covering the Full Tract
If your doctor needs a view of the small intestine without the complexity of balloon enteroscopy, capsule endoscopy is often the solution. You swallow a pill-sized camera that takes thousands of photos as it moves through your entire digestive tract under its own power, propelled by normal muscle contractions. It’s especially useful for the small intestine, the region that traditional scopes struggle to reach.
The capsule doesn’t stop at any set distance. It travels the full length of the GI tract, from esophagus to rectum, typically over 8 to 12 hours. The trade-off is that it can only take pictures. It can’t take tissue samples, remove polyps, or treat anything it finds. If the capsule spots something abnormal, you may still need a traditional scope or balloon enteroscopy for a closer look or treatment.
How Scope Size Changes for Children
Pediatric endoscopy uses the same types of procedures, but scope diameter is scaled to the child’s size. Infants under 5 kilograms (about 11 pounds) are examined with ultrathin scopes around 6 millimeters wide. Children between 5 and 20 kilograms typically get a slimmer 9-millimeter gastroscope. Kids over 20 kilograms can often tolerate a standard adult-sized scope.
For colonoscopy, the scaling follows a similar pattern: the smallest patients may be examined with an ultrathin gastroscope used as a substitute colonoscope, while children over 20 kilograms use a pediatric or even adult colonoscope with a working length of about 168 to 170 centimeters. The distances traveled are shorter simply because the anatomy is smaller, but the goal is the same: reach the cecum for a complete exam.
Quick Comparison by Procedure
- Upper endoscopy (EGD): ~60 cm from the teeth to the duodenum
- Colonoscopy: ~150–170 cm from rectum to cecum
- Push enteroscopy: 40–120 cm past the stomach into the small intestine
- Balloon enteroscopy: potentially the full length of the small intestine (up to 6 meters combined with oral and rectal approaches)
- Capsule endoscopy: the entire GI tract, roughly 9 meters total
The type of endoscopy your doctor recommends depends entirely on where the problem is suspected. Most people will only ever need the two common procedures, the upper endoscopy and the colonoscopy, which together cover the esophagus, stomach, first part of the small intestine, and the entire large intestine.