1. Time
   Pressure
2. Temperature
   Force

A megasecond is one billion seconds, and a millisecond is one thousandth of a second. A nanosecond is one billionth of a second, and Planck time is the smallest unit of measurement. Planck time is the time that it takes for light to travel one Planck length.

1. Electric current
   Temperature
2. Area
   Frequency

The Celsius temperature scale is also known as the centigrade temperature scale because of the 100-degree intervals between the freezing point at the 0 degrees and the boiling point at 100 degrees. The Swedish astronomer Anders Celsius developed the scale in 1742.

1. Force
   Electric current
2. Temperature
   Liquid volume

An ampere is a basic unit of electric current in the International System of Units (SI). The ampere was named for French physicist and mathematician Andre-Marie Ampere, and it expresses a stream of one coulomb of electricity per second.

1. Radioactive decay
   Density
2. Amount of a substance
   Luminous intensity

Mole is also written as "mol" in chemistry, and is the unit used for measuring sizable quantities of of small particles such as atoms and molecules. The number of particles in one mole is the same for all substances.

1. Sound
   Mass
2. Electricity
   Volume

Decibel is the unit of measurement for sound used to describe electrical signals, and it is expressed as a proportion between two tangible quantities, usually electrical and acoustical power. Decibel also measures sound intensity.

1. Sound
   Density
2. Energy
   Area

Joule is a measurement of energy derived when one newton force acts on an object in the same motion direction through one meter of distance. Joule also represents the amount of heat energy released when one ampere of electric current flows through an electrical resistance of one ohm per second.

1. Electricity
   Liquid volume
2. Angle
   Power

Horsepower (hp) is the unit measurement for power, or the rate at which work is done. It has been defined as the weight that a horse could raise 1 foot in 1 second. One horsepower is equal to 746 watts.

1. Heat energy
   Length
2. Density
   Radiant flux

Calorie is the amount of heat necessary to raise the temperature of 1 milliliter of water 1 degree Celsius, from 14.5 degrees to 15.5 degrees Celsius. Calories measure food energy and the stored energy of living beings.

1. Liquid volume
   Mass
2. Refractive lens power
   Sound

Diopter, or dioptre, describes the optical power of a given lens or any curved mirror. Diopter is equal to the reciprocal, or the inverse, of the focal length (in meters). Diopter equals 1000 divided by focal length (in millimeters).

1. Paper quantity
   Temperature
2. Electrical capacitance
   Refractive index

A farad is equal to a capacitor's capacitance, where one coulomb causes a potential difference of one volt. Electrical capacitance is the capability to maintain a charge. The unit is named for English scientist Michael Faraday.

1. Luminous intensity
   Frequency
2. Radioactive decay
   Temperature

The becquerel measures the activity of a given quantity of radioactive substance where one nucleus decays every second. Nucleus decay amounts to one spontaneous transition. The becquerel is named for French physicist Antoine Henri Becquerel.

1. Electrical conductance
   Stress
2. Heat
   Frequency

Regarding a direct current, siemens conductance is the inverse of the resistance measured in ohms, where siemens equals amperes per volts. Siemens for an alternating current is the inverse (in ohms) of the total opposition which a circuit (whole or part) exhibits to electrical current.

1. Magnetic flux
   Electric voltage
2. Quantity
   Volume

Volt is the difference of electrical potential, electromotive force or potential difference between two points in a conductor carrying one ampere current, where the released power between the two points is one watt. This unit is named for Italian scientist Alessandro Volta.

1. Electrical inductance
   Power
2. Refractive index
   Radiant flux

Henry is a unit that measures either mutual inductance or self-inductance. In the case of mutual inductance, one henry equals the value of two coils positioned so that an electromotive force of one volt is generated in one coil when the current in the other coil is changing one ampere per second.

1. Frequency
   Heat
2. Mass quantity
   Force

A bale is a large bundle of identical individual items tightly bound to facilitate weighing, storage, cataloging, sale or transport. Cotton, paper and hay quantities are measured by the bale. One ream of paper totals 500 sheets of paper.

1. Time
   Group quantity
2. Electric current
   Area

In earlier times, a dozen of 12 was a practical way to quantify a group of easy-to-count and carry loose identical items. The word "dozen" comes from the Latin "duodecim," which means "twelve."

1. Electric charge
   Weight
2. Pressure
   Thermodynamic temperature

Pascal (Pa) measures pressure as one kilogram per meter per second squared or one newton per square meter. Pascal also measures stress, Young's modulus (numerical constant) and tensile strength, which is the maximum load that a material can sustain without breaking divided by the material's initial cross-sectional area.

1. Force
   Area
2. Angle
   Refraction

One newton describes the force needed to give one kilogram of mass an acceleration of one meter per second squared in the direction of an applied force. The unit is named for English scientist and mathematician Sir Isaac Newton.

1. Density
   Frequency
2. Weight
   Electrical conductance

Hertz is a derived unit of frequency in the S.I. system that equals one cycle per second. Periodic phenomena are measured by hertz, which gauges if one cycle of the same phenomenon repeats in a one-second period. A gigahertz equals 1000 million hertz. The unit is named for German physicist Heinrich R. Hertz.

1. Liquid volume
   Mass quantity
2. Land area
   Force

An acre is equal to 160 square rods (old English measurement), 4,840 square yards or 43,560 square feet. A hectare is a unit of area that equals 100 ares (100 square meters), 10,000 square meters or 2.471 acres.

1. Electrical inductance
   Radioactive decay
2. Weight
   Magnetic flux

A weber was named for German physicist Wilhelm Eduard Weber. One weber equals 1 volt-second. A weber expresses the flux quantity produced within itself by an electromotive force of 1 volt as the flux reduces to zero at a consistent rate within 1 second.

1. Density
   Hotness level of chili peppers
2. Color saturation of chili peppers
   Liquid volume

The Scoville scale measures the relative spiciness or heat of chili peppers and other spicy foods. Pharmacist Wilbur Scoville devised the Scoville heat unit (SHU) in his pursuit to create a heat-generating ointment. The SHU is based on the amount of dilution necessary to eliminate the "hotness" of a substance.

1. Size
   Weight
2. Chance of sudden death
   Force

Micromort measures the risk of human death from engagement in everyday activities. The unit is defined as a one-in-a-million chance of sudden death which enables medical doctors to more effectively compare intervention risks with the risks of other activities.

1. Angle
   Sound
2. Liquid volume
   Temperature

The symbol "rad" represents the mathematics S.I. unit radian. A radian is the intersection of two radii at a circle's center, where the angle's arc is equal to the length of the radius.

1. Electric current
   Angle
2. Luminous intensity
   Pressure

Candela is used in physics, and it expresses the luminous intensity in a certain direction from a source that emits monochromatic radiation with a frequency of 540 trillion hertz and a radiant intensity in that direction of 1/683 watt per steradian. But you probably knew that, right?

1. Force
   Weight
2. Temperature
   Sound

In earlier times, the stone unit was a relative unit of measure used to weigh products. Today, the stone is used to measure large quantities (especially people and animals) and is equivalent to 14 pounds.

1. Volume
   Sound
2. Area
   Mass

A tonne also equals a metric ton, and a hundredweight is equivalent to one twentieth of a ton. There are probably more "odd" measurements when it comes to weight and mass than anywhere else, because of their use in early commerce.

1. Sound
   Astronomical distance
2. Density
   Area

One parsec is equal to approximately 3.26 light years. The parsec correlates to the range at which earth's orbit's mean radius subtends an angle of one second of arc.

1. Interest rate
   GDP
2. Purchasing-power parity
   Debt

The "Big Mac Index" contrasts the purchasing-power parity (PPP) of different countries based on the price of a similar item, like the "Big Mac." The PPP is then compared with actual currencies to gauge which currencies are overvalued or undervalued when compared with the U.S. dollar.

1. Land area
   Sound
2. Liquid volume
   Water temperature

One gallon of liquid equals 3.79 liters. A liter measures liquid volume equal to approximately 1.75 pints, and a fluid ounce is one sixteenth of a U.S. pint (roughly 0.03 liter).

1. Weight
   Power
2. Frequency
   Temperature

The watt is a S.I. unit of power that equals one joule per second. The watt correlates to an electric circuit's capacity, where the potential difference is one volt and the current is one ampere.

1. Thermodynamic temperature
   Liquid volume
2. Sound
   Density

Kelvin equals 1/273.16 of the triple point water's thermodynamic temperature. The kelvin's magnitude equals that of degree centigrade (Celsius). Degree Celsius temperature is expressed as numerically equal to the temperature in kelvins reduced by 273.15.

1. Amount of a substance
   Temperature
2. Magnetic flux density
   Group quantity

The tesla is a derived unit of magnetic flux density, as well as magnetic field strength. The tesla more suitably measures strong magnets, and the gauss unit is used when measuring the strength of small magnets.

1. Force
   Density
2. Radiant flux
   Thermodynamic temperature

In physics, torque, also called the moment of force, changes the rotation rate of a body. Units that express torque are units of force multiplied by distance, such as pound-foot.

1. Electric charge
   Sound
2. Land area
   Weight

One coulomb equals one ampere multiplied by one second. The U.S. standard for one coulomb is the amount of electric charge transferred by a current of 1 ampere in 1 second, which is equivalent to 1 ampere-second.