Thermal energy is measured using a thermometer. We use thermometers to find the temperature of a substance. Temperature is actually a measure of the substance's thermal energy.
Inside a thermometer is a liquid (most often alcohol) that, when heated, expands and rises through the thermometer. We read this as an increase in temperature. This also indicates an increase in thermal energy. When thermal energy is decreased, the liquid contracts and falls through the thermometer. We read this as a decrease in temperature and thermal energy.
more thermal energy = higer temperature
less thermal energy = lower temperature
There are three main scales that the world uses to measure temperature: Fahrenheit (ºF), Celsius (ºC), and the Kelvin Scale (K). We're going to focus on the Fahrenheit and Celsius scales. Each scale uses different temperatures to measure the boiling point and freezing point of water. Below is a table that shows how the scales differ.