How big is the catheter used during esophageal manometry?

Small compared: With food that you typically eat and swallow and smaller then most endoscopes for traditional endoscopy. The manometry catheter is designed to go into the nose so it has to be small. However, some technicians will let you swallow the tube through the mouth which may make it easier. Worth asking....

HUGE...: Bigger than a rain gutter... No - seriously it is small enough to slip through your nostril and go down the back of your throat into your esophagus.

4 mm diameter: Esophageal manometry catheters are typically about 4 mm in diameter. They are long enough to travel from your nose, down the esophagus and into the stomach.