How To Read A Mercury Thermometer?


Do you want to acquire the skill to perform essential first aid procedures? Are you a non-medical person wanting to learn this procedure? Do you want to learn the specific steps on how to read a mercury thermometer? If your answers to these questions are in the affirmative, then continue reading, because this post will provide you this crucial information.

If you can learn these steps, you can use this crucial information during emergency situations in which the patient is febrile. You may not be a nurse or a doctor, but learning this skill will be beneficial to you and to the people around you, ultimately. Simply put, you could save a life.

What is the Mercury Thermometer?

This is an elongated device, measuring around 3 inches that uses mercury to measure body temperatures in degree Celsius or Fahrenheit.

The parts of the thermometer are the bulb containing the mercury, the contraction chamber, the main scale, the stem and the expansion chamber.

  • In the Celsius scale, the short lines correspond to 0.1 degrees, and the long lines indicate 1 or 0.5 degrees.
  • In the Fahrenheit scale, the short lines correspond to 0.2 degrees and the long lines indicate 1 degree.

The normal temperature in Celsius is 36.5 to 37.5 degrees, while the normal temperature in Fahrenheit is 97.7 to 99.5 degrees.


In obtaining the temperature, you will need the following materials:

  • 70% isopropyl alcohol
  • Cotton or gauze pad
  • Soap
  • Water
  • Gloves
  • Mercury thermometer (glass or plastic)
  • Writing materials

You should also know that there are different types of mercury thermometers, these are:

  • Rectal thermometers – These are usually used for children. You can differentiate them from the oral thermometers because their bulbs are generally rounded.
  • Oral/axilla thermometers – These are used for adults. The bulbs are commonly elongated.

I recommend the use of disposable thermometers because you will be rest assured that they are sterile and clean and, at the same time, you won’t go through the trouble of cleaning them up after use. You used them only once and discard them properly.

So far, so good? It’s easy, right?

Let’s now proceed to the actual steps in learning how to read a mercury thermometer. Remember the data about the parts and the most common types of mercury thermometers because I will refer to them later on.

Steps on How to Read a Mercury Thermometer

Step #1 - Check the Mercury Thermometer for Any Defects


Wear your gloves and carefully examine the mercury thermometer if there are no chips or broken parts. Make sure also that you are using the appropriate thermometer for the body part intended. For example, if you plan to obtain the oral temperature, you should be using an oral thermometer, or a rectal thermometer for the anal opening.

Mercury is an extremely toxic substance and any contact with the raw material can cause heavy metal poisoning. This can be fatal to your body. When a mercury spill occurs, bring the person to a doctor immediately - even without waiting for the symptoms to manifest. As the cliche goes: “It’s better to be safe than sorry”.

Step #2 - Clean the Mercury Thermometer before Use

The mercury thermometer can be made of glass or plastic. Nowadays, the plastic is preferable because it eliminates the danger of breakages. Anyway, whatever material the thermometer is made of, you have to clean it thoroughly first before use. You can do this by using 70% isopropyl alcohol, then washing it with soap and water. You can use cotton balls when cleansing and wiping.

Step #3 - Shake the Thermometer to Assure Accurate Readings

Bring the thermometer at your eye level and take note of the reading. You can turn the thermometer sideways until you can see the reading. The reading should be lower than 96 degrees Fahrenheit or 36.5 degrees Celsius. If not, shake the thermometer downwards until the mercury goes down below 96 degrees Fahrenheit or 36.5 degrees Celsius.

This will ensure that your reading of the body temperature will be accurate. Ascertain that you have a good grip of the stem because it might slip out of your fingers.

Step #4 - Insert the Thermometer


For oral mercury thermometers

Allow the patient to be seated or to lie down in a supine position. You can now insert the bulb of the thermometer under the tongue, with the stem positioned sideways from the mouth.

Instruct the patient not to bite the device and to close his lip gently. Let the thermometer stay under the tongue for 3 minutes. (Some thermometers need only a minute, so read the manufacturer’s literature that comes with the thermometer.)

For axilla mercury thermometers

Using a clean gauze pad or tissue, pat dry the person’s armpit before inserting the thermometer. The thermometer must be angled toward the head and placed firmly inside the armpit with the bulb at the center of the axilla.

Cross the person’s arm on his chest with the direction going upwards to secure the thermometer. The patient can lie down or stay seated. Maintain that position for 10 minutes.

For rectal mercury thermometers (children)

This procedure is typically used with children. The steps are similar to the steps in taking the oral temperature, only, this time the thermometer is inserted into the anal opening.

Apply a lubricant to the bulb of the thermometer by using a gauze pad. Don’t dip the thermometer directly into the lubricant because this can contaminate it. The lubricant will allow the easy entry of the thermometer into the anus.

Let the child lie down in a supine position. Raise both of his legs and insert the thermometer slowly into the rectal opening up to ½ or ¾ inches of its length. The stem should be held firmly between your fingers. Hold it in that position for 2 minutes.

Another position is to hold the child firmly on top of your lap, while you obtain the temperature.

For rectal mercury thermometers (adults)

For taking the rectal temperatures in adults, the steps are the same as that of infants, only the position varies. The adult can be lying down on his side with his anal opening exposed with the help of your other hand. While the thermometer is held in your right hand, your left hand can assist in spreading the folds of the buttocks to expose the anus.

Step #5 - Read the Temperature


After three minutes, wipe swiftly the thermometer with a gauze pad, cotton or tissue. The movement should be from the stem downwards to the bulb. Be careful not to touch the bulb.

After wiping, hold the stem of the thermometer at eye level and turn it back and forth until you see the red, blue or silver-colored line. Read the temperature on the nearest line using the guideline given previously. Write down your result. Double check if your entry is correct.

Step #6 - Clean the Thermometer

Clean the thermometer thoroughly using 70% isopropyl alcohol, then soap and water, and then return it to its case. Dispose of your gloves and used materials in their appropriate containers or trash cans. If the thermometer is disposable, you have to dispose of it properly too.

Step #7 - Perform after Care on the Person

After obtaining his temperature, check the condition of the person and ensure that he is comfortable and clean.

Step #8 - Wash Your Hands

Always remember to wash your hands thoroughly after each procedure. Diseases can be transmitted easily through fecal waste materials.


Did you enjoy this tutorial? I hope you did. Keep in mind what type of thermometer is appropriate for the rectum and the mouth. You wouldn’t want a nasty mix-up between the two, would you?

Again, ensure that you don’t get exposed to mercury because it’s toxic.

Knowing how to perform some basic first aid skills, such as reading temperatures will not only benefit you but other people as well. You can now contribute positively towards the maintenance of good health and well-being.

If you have any ideas or observations about the steps on how to read a mercury thermometer, feel free to express them on the comment’s section below. We want to read your two cents’ worth.


Hello everyone! I’m glad to have you here. I’m a medical technologist by profession. My second love is writing. So, I’m focusing on providing content to help other people with their health problems. I hope I can be of help to you.

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