Did you know that the highest recorded surface temperature recorded on Earth is a sweltering 134 degrees Fahrenheit (56.7 degrees Celsius)? And that the lowest recorded temperature is a freezing minus 128 degrees Fahrenheit (minus 89 degrees Celsius)? You can imagine how extreme these temperatures are when you consider that the average surface temperature on Earth is 57 degrees Fahrenheit (14 degrees Celsius).
Air temperature is traditionally measured using liquid thermometers containing mercury. These types of thermometers are narrow glass tubes in which the red-coloured liquid (which could also be alcohol) rises up the tube from a glass bulb as it expands with heat and contracts, and goes back down into the bulb when the temperature falls. The tube has standardized readings printed on the outside, which often show both the Fahrenheit and Celsius temperature scales. A maximum thermometer is an important type of thermometer which is commonly used to measure body temperature. When the temperature rises or drops, the liquid doesn’t rise or fall straight away, which means the reading can be observed for some time after it is removed from the environment in which it was taken.
Some other types of thermometers include electronic thermometers, probe thermometers and bimetallic strip thermometers. There are also various specialized thermometers, for example, cryometer thermometers, infrared thermometers, K-type thermometers, nanothermometers, pill thermometers and temperature data loggers.
But what if you want to measure temperature without a thermometer? If you want to know how hot or cold something is, there are several other devices you can use. In this article, we’ll reveal what these are.
If you don’t have a thermometer, you can measure body temperature by touch and air temperature using an app on your mobile phone.
Three other devices that are used to measure temperature are Langmuir probes, pyrometers and resistance temperature detectors (RTDs).
Continue reading to find out more about measuring temperature without a thermometer.
Temperature measurement is important in a number of different scenarios. Some of these are medical, some are climatical, and others are scientific.
- Medical — Body temperature is measured to determine whether a person has a fever before the appropriate treatment can be administered.
- Climatical — From dressing appropriately for the weather to preparing a country for a heatwave, it is extremely useful to be aware of the temperature outside.
- Scientific — In laboratories, temperature measurement is essential for controlling distillation processes, determining the purity of substances by their boiling points and melting points and establishing the flash points of flammable oils.
There are five ways you can measure temperature, even without a thermometer:
This is not the most accurate way to measure temperature because it cannot give you a specific reading. However, if you think you may have a fever, you can ask someone to touch your forehead, chest and back to see whether you feel hotter than normal.
Touching the forehead with the back of the hand to see whether it feels hot is one of the first things most people do when they suspect a fever. The person who has the suspected fever won’t always be able to tell whether their own forehead is hotter than normal as, usually, their entire body feels hot. So, rather than taking their own temperature, they should always have someone else do it for them. A person can also check the temperature of someone’s forehead by resting their cheek against it.
If you do think you have a temperature, it is vital that you confirm this using a thermometer and seek medical attention. The average body temperature is 98.2 degrees Fahrenheit (36.8 degrees Celsius), with a fever occurring when the body’s temperature exceeds 100.4 degrees Fahrenheit (38 degrees Celsius).
Later, we’ll explain how to take your own or someone else’s body temperature using a thermometer, but for now, here are some of the other signs to look for if you think you or someone else has a fever:
- Flushed cheeks — If the person with the suspected fever has reddish or purple cheeks (or just more color than usual), it could be an indication that they are burning up from a fever.
- Pinching the hand — Sometimes, being dehydrated is a sign of fever. You can check for dehydration by pinching the back of the hand to see whether the skin moves back into place quickly (which suggests the person is hydrated) or slowly (which suggests the person is dehydrated).
- Checking urine color — Another way to check for dehydration is by looking at urine color. Dark yellow or orange urine that may also have a strong smell is a sign of dehydration.
- Other symptoms — Such as:
- Body aches
- Difficulty concentrating
- Loss of appetite
- Muscle aches
- Sore eyes
- Swollen lymph nodes
- Weak muscles
2. Mobile phone
While most smartphones do not have built-in thermal sensors — which means they cannot measure air temperature — there are apps you can download to estimate the temperature of a room or outside.
Weather apps, for example, use weather data based on the GPS location of the device. And apps like Room Temperature Thermometer for Android devices or Real Thermometer for iOS devices work in the same way.
Some apps are more accurate as they work with a sensor that plugs into the outside of a smartphone to provide a localised temperature reading. However, they are not widely available and are quite expensive to buy.
3. Langmuir probe
These temperature-measuring devices are used by scientists to determine the electron temperature, electron density and electric potential of a plasma.
One or more electrodes are inserted into a plasma, and constant or intermittent readings are taken to determine the physical properties of the plasma.
These devices are used to measure the temperate of objects at a distance. They were widely used by the medical profession to take people’s temperature during the COVID-19 pandemic.
They can determine the temperature of matter by the amount of thermal radiation it emits. This process is known as “pyrometry” or “radiometry”.
5. Resistance temperature detector (RTD)
Although they can also be constructed in other ways, an RTD typically consists of a fine wire wrapped around a heat-resistant core and housed in a protective probe. The wire that’s used will be a pure material, for example, copper, nickel or platinum.
Because of their accuracy, RTDs are replacing thermocouples in industrial applications below 1,112 degrees Fahrenheit (600 degrees Celsius).
As stated in the previous section, it is important to know someone’s exact temperature for medical reasons. If you think you have a fever, the best way to confirm this is to use a thermometer.
There are four ways to check for a fever using a thermometer:
Oral thermometers are placed inside someone’s mouth, where they should rest for about 20 seconds under the tongue and as close to the centre of the mouth as possible.
Once the reading has been taken, the person’s temperature will be displayed.
Most modern oral thermometers are easy to use, as they are digital and will beep to let you know when they’ve completed a reading.
Lubricant is added to the tip of a rectal thermometer and then inserted about half an inch into the rectum. If you don’t have a thermometer specifically designed for rectal use, you can use an oral one.
While they may not be the easiest or most comfortable types of thermometers, they do provide highly accurate readings. This makes them a good option when taking an infant’s temperature because, if you suspect they have a fever, it is vital that you get an accurate reading.
On the forehead
There are two types of forehead thermometers. One is a plastic strip that’s placed on the forehead and tells you whether the person’s temperature is high or low (note that it doesn’t give an exact reading), while the other is placed on the middle of the forehead and measures the person’s temperature using infrared light.
They may not be as accurate as rectal thermometers, but forehead thermometers are becoming more common in the home and are a particularly good option for children, as they don’t require them to be still for long.
In the ear
Ear thermometers are inserted into the ear with the sensor pointing inwards and down the ear canal towards the eardrum. The thermometer is then turned on to give a reading in just a few seconds.
These types of thermometers are less accurate than others, but, again, they are a good option if you need to take a child’s temperature as they don’t require them to sit still for a long period of time.
Temperature is measured in three main scales. These are the Fahrenheit scale, the Celsius scale and the Kelvin scale. The Fahrenheit and Celsius scales use degrees to measure temperature in everyday situations, while the Kelvin scale is used in science and engineering.
The Fahrenheit scale
The United States is one of only three countries in the world that use the Fahrenheit Scale to measure temperature. This is because the US uses the imperial system of measurement (as do Burma and Liberia).
The Fahrenheit scale was developed by the Polish physicist Daniel Gabriel Fahrenheit, who also invented the mercury and alcohol liquid thermometers.
The Celsius scale
Every other country in the world uses the Celsius scale to measure temperature. This is because it is part of the metric system, which is the official measurement system for most countries.
Whether they are from a country that uses the imperial system or the metric system, all scientists use the Celsius or Kelvin scale to measure temperature. This is so they can understand and compare theories, experiments and ideas and share data with one another quickly and easily.
What is the difference between Celsius and Centigrade?
There is no difference between Celsius and Centigrade; Centigrade is just the old-fashioned name for Celsius.
The Kelvin scale
As mentioned, the Kelvin scale is used in science and engineering. It is used to record precise temperatures and is essential for calculating temperatures in outer space.
Other temperature scales
Some of the other temperature scales include the Delisle scale, the Newton scale, the Rankine scale, the Rømer scale and the Réaumur scale.
If you don’t have a thermometer, you can measure temperature in the following ways:
- Touch — If you think you may have a fever, you can ask someone to touch your forehead, chest and back to see whether you feel hotter than normal. Touching the forehead with the back of the hand to see whether it feels hot is one of the first things most people do when they suspect a fever, but the temperature of the forehead can also be checked by resting a cheek against it.
- Mobile phone — Weather apps and apps like Room Temperature Thermometer for Android devices or Real Thermometer for iOS devices use weather data based on the GPS location of the device to estimate the temperature of a room or outside. Apps that work with a sensor which plugs into the outside of a smartphone to give you a localised temperature reading are more accurate, however, they are expensive and not widely available.
- Langmuir probe — These are used by scientists to determine the electron temperature, electron density and electric potential of a plasma.
- Pyrometer — Pyrometers are used to measure the temperate of objects at a distance. They were widely used by the medical profession to take people’s temperature during the COVID-19 pandemic.
- Resistance temperature detector (RTD) — Typically, an RTD consists of a length of fine wire which is wrapped around a heat-resistant core and housed in a protective probe. Because of their accuracy, they are replacing thermocouples in industrial applications below 1,112 degrees Fahrenheit (600 degrees Celsius).