The Metric System

• The metric system, also known as the International System of Units (SI), is a globally recognized system of measurement used for standardizing units of measurement for various physical quantities. 

• It originated in France during the late 18th century and was officially developed during the French Revolution. 

• The metric system was created to address the need for a consistent and decimal-based system of measurement, as the existing systems in use at the time were often based on arbitrary and inconsistent units.

• Length: meter (m)

• Mass: kilogram (kg)

• Time: second (s)

• Electric current: ampere (A)

• Temperature: kelvin (K)

• Amount of substance: mole (mol)

• Luminous intensity: candela (cd)

SI Units

Volume:

• • Cubic Meter (m³) is the standard unit for volume in the Metric System.

  • Liter (L) is a more commonly used unit for smaller volumes.

Density:

• Kilogram per Cubic Meter (kg/m³) is the standard unit for density in the Metric System.

Energy:

• Joule (J) is the standard unit for energy in the Metric System.

US customary

Volume:

• • Cubic Inch (in³) is commonly used for small volumes.

  • Cubic Foot (ft³) is often used for larger volumes.

Density:

• Pounds per Cubic Inch (lb/in³) is used for density in the American system.

Energy:

• • British Thermal Unit (BTU) is a common unit for energy in the American system.

  • Foot-pound (ft-lb) is another unit used for energy, especially in mechanical applications.

Other US Customary Units:

• Length: inch (in), foot (ft), yard (yd), mile (mi)

• Mass (technically weight): ounce (oz), pound (lb), ton (short ton)

• Time: second (s), minute (min), hour (hr) — same as SI

• Temperature: degree Fahrenheit (°F)

• Volume: fluid ounce (fl oz), cup (c), pint (pt), quart (qt), gallon (gal)

• Lumen (lm): Measures luminous flux (total light output).

• Foot-candle (fc): Measures illuminance (light falling on a surface). 1 foot-candle = 1 lumen per square foot.

• Candela (cd): Still used for measuring the intensity of light in a particular direction.

A calorie is a unit of energy. Specifically, it is the amount of energy required to raise the temperature of one gram of water by one degree Celsius. There are two common units of calories:

• Small calorie (cal): The amount of energy needed to raise the temperature of one gram of water by one degree Celsius.

• Kilocalorie (kcal or Cal): This is often used in the context of food and nutrition. It is equal to 1,000 small calories and is the amount of energy needed to raise the temperature of one kilogram of water by one degree Celsius.

https://www.nist.gov/pml/weights-and-measures/metric-si/si-units 

https://www.nist.gov/pml/weights-and-measures/metric-si-prefixes