Using a thermometer to check your temperature can help you manage an illness. A rise in your temperature is usually caused by an infection. When using any kind of thermometer, make sure you read and follow the instructions that come with the thermometer.

Normal body temperature

Normal body temperature is about 98.6 degrees Fahrenheit (°F) or 37 degrees Celsius (°C). Your temperature often varies from 1 to 2 °F or ½ to 1 °C. Your temperature is usually lower in the morning and increases during the day. It reaches its high in the late afternoon or evening.

Using a digital thermometer

Digital Thermometer

You can get fast and accurate readings with digital thermometers. They are available in many shapes and sizes at grocery stores, department stores, and drug stores. You can use a digital thermometer in three ways:

  • Oral (in the mouth)
  • Rectal (in the bottom)
  • Axillary (under the arm)

Do not use the same thermometer for both oral and rectal readings. Be sure to label your thermometer either “oral” or “rectal” to know the difference.

Taking your temperature orally with a digital thermometer

  1. Wash your hands with soap and warm water.
  2. Use a clean thermometer, one that has been washed in cold water, cleaned with rubbing alcohol, and then rinsed to remove the alcohol.
  3. Do not eat or drink anything for at least five minutes before you take your temperature. You should keep your mouth closed during this time.
  4. Place the thermometer tip under the tongue.
  5. Hold the thermometer in the same spot for about 40 seconds.
  6. Readings will continue to increase and the F (or C) symbol will flash during measurement.
  7. Usually, the thermometer will make a beeping noise when the final reading is done. If you are keeping track, record the temperature and the time.
  8. Rinse thermometer in cold water, clean it with alcohol, and rinse again.

When to call your health care provider

Call your health provider if you have a temperature of 100.4° F (38° C) or higher. This could be a sign of infection and should be treated right away.

Call your health care provider right away if you have a fever and:

  • Severe headache
  • Stiff neck
  • Swelling of your throat
  • Confusion


© Copyright 1995-2016 The Cleveland Clinic Foundation. All rights reserved.

This information is provided by the Cleveland Clinic and is not intended to replace the medical advice of your doctor or health care provider. Please consult your health care provider for advice about a specific medical condition. This document was last reviewed on: 8/9/2016...#9959