Buzz
Flatus—the technical term for gas released from the intestines—has been the subject of humor, countless YouTube videos, and college dorm room conversations worldwide. Yet, the volume of a fart is rarely discussed. The gases that make up a fart—mainly nitrogen, hydrogen, carbon dioxide, oxygen, and methane—have mass, making it theoretically possible to measure a fart’s volume. But, has anyone actually done it? And if so, how?
Indeed, they have. In 1991, a team of gastroenterologists from the Human Gastrointestinal Physiology and Nutrition Department at the Royal Hallamshire Hospital in Sheffield, England published a study in the journal Gut attempting to measure the size of flatulence. Their method was straightforward: 10 volunteers consumed 200 grams of baked beans in addition to their regular diet, and their flatulence was monitored over a 24-hour period using rectal catheters.
Out of sight of the sun's rays. MediQuip
To ensure their data collection method was reliable, participants sat in a bath with a rectal catheter inserted, connected to a gas bag. After they passed gas, the absence of visible bubbles confirmed that the catheter was sealed.
The doctors found that the average adult expels about 705 milliliters of gas daily (around 24 ounces, or two cans of soda). There was no significant difference between men and women, though the volume of farts tended to be larger after meals.
The individuals had a wide range of gas output, from 476 ml to 1491 ml in 24 hours. The study showed that a single fart, regardless of time, gender, or body size, typically ranged from 33 to 125 ml, with an average of 90 ml. That’s about three ounces of humor.
Dr. Matthew Bechtold, a gastroenterologist and associate professor at the University of Missouri, explains that fart volume varies significantly depending on how much air is swallowed and the gases produced by bacteria in the colon. Carbohydrates that are not fully digested feed these bacteria, which then release gases. “Raffinose, a sugar found in cabbage and broccoli, is a major contributor to flatulence because it is poorly digested,” he says.
The study observed that volunteers on low-fiber diets had a significant reduction in the gases produced by fermentation, leading to a fart volume of just 200 ml over the course of a day.
The researchers did not clarify whether solid matter should be included when measuring fart mass. According to Bechtold, typically no fecal matter escapes during the passing of gas. “The anus does a good job of keeping solids in while letting gas out,” he explains.
The approximate volume of an average fart.
With that question answered, we posed another fart-related inquiry to Bechtold: If someone were to pass gas in cold weather with their pants down, could the fart be visible, similar to how we see breath in cold air?
“Since the gas is contained in an environment at 98 degrees Fahrenheit, much like the lungs, if it’s passed in cold weather, it could likely be visible,” he says. “However, since most people are dressed, with pants acting as a barrier, the gas usually goes unnoticed and diffuses quickly into the air.”
To put it differently: A fart is about the size of an airport-approved travel bottle, and it might be visible in cold weather—if you're willing to remove your pants for the sake of science.
