The amount of mercury in a thermometer is about 3 grams. A mercury thermometer is used to measure the body temperature.
The amount of mercury present in a thermometer is very small. According to NHS, a typical thermometer that is used to measure body temperature contains not more than 3 grams of mercury.
The typical fever thermometer contains 0.5 to 3 grams of elemental mercury. Inhaling the vapors of this liquid mercury can cause serious health issues in otherwise healthy person. So, the use of mercury thermometer has been banned for medical purposes in most countries since 2012.