4,046.86

One acre comprises 4,840 square yards, 43,560 square feet or about 4,046.86 square meters (0.404686 hectares).

The word "acre" is derived from Old English cer originally meaning "open field", cognate to west coast Norwegian kre and Swedish ker, German acker, Latin ager, and Greek αγρ (agros).

881000

Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure. The speed of light in a vacuum corresponds to a Mach number of approximately 881,000 (relative to air at sea level).

1.852

1knot is defined as 1.852 km per hour. In actual, this unit is defined equivalent to 1 nautical mile per hour.

473.176

The pint is an English unit of volume or capacity in both the imperial system and in United States customary units. The imperial version is 20 imperial fluid ounces and is equivalent to about 568 ml, while the U.S. version is 16 U.S. fluid ounces and is equivalent to about 473 ml. Thus the traditional British pint of beer is approximately 20% larger than the American pint. One imperial pint is equal to 19.2152 US fluid ounces.

250

The definition of volume of a cup differs depends on the unit; the metric cup is equivalent to 250 milliliter, the US customary cup is 236.588, US legal cup is 240, the imperial cup is 248, and Japanese cup is 200.
There is no internationally-agreed standard definition of the cup, whose modern volume ranges between 200 and 284 millilitres.

6.35

The stone was originally used for weighing agricultural commodities. Historically the number of pounds in a stone varied by commodity, and was not the same in all times and places even for one commodity. Potatoes, for example, were traditionally sold in stone and half-stone (14-pound and 7-pound) quantities.
This is defined in British legislation as being a weight or mass equal to 14 avoirdupois pounds (about 6.35 kilograms).

28.35

1 ounce is equivalent to 28.35 gram. Ounce derives from Latin uncia, a unit that was one twelfth (1/12) of the Roman pound (libra). Ounce was borrowed twice: first into Old English from an unattested Vulgar Latin form with ts for c before i (palatalization) and second into Middle English through Anglo-Norman and Middle French.

0.32745

1 pound is equivalent to 0.32745 kilo gram.

The abbreviation of pound is lb. The letters Lb for pound come from a Latin word for an ancient Roman unit of weight, libra.

304.8

Some believe that the original measurement of the English foot was from King Henry I, who had a foot 12 inches long; he wished to standardize the unit of measurement in England. Though there are records of the word "foot" being used approximately 70 years before his birth, it is supposed that this old standard was redefined ("calibrated") according to Henry's foot. In fact, there is evidence that this sort of process was common before standardization. A new, important ruler could try to impose a new standard for an existing unit, but it is unlikely that any king's foot was ever as long as the modern unit of measurement.

In actual, the average foot length is about 9.4 inches (240 mm) for current Europeans. Approximately 99.6% of British men have a foot that is less than 12 inches long. One attempt to "explain" the "missing" inches is that the measure did not refer to a naked foot, but to the length of footwear, which could theoretically add an inch or two to the naked foot's length. This is consistent with the measure being convenient for practical uses such as building sites. People almost always pace out lengths while wearing shoes or boots, rather than removing them and pacing barefoot.

Now, the foot in SI unit is equivalent to 304.8 mili meter.

25.4

The origin of the inch is disputed. Historically, in different parts of the world (even different cities within the same country) and at different points in time, the inch has referred to similar but different standard lengths.

The English word inch comes from Latin uncia meaning "one twelfth part" (in this case, one twelfth of a foot); the word ounce (one twelfth of a troy pound) has the same origin. The vowel change from u to i is umlaut; the consonant change from c (pronounced as k) to ch is palatalization (see Old English phonology).

Anyway, the one inch is equivalent to 25.4 mili meter.

1852

The nautical mile was originally defined as one minute of arc along a meridian arc of the Earth. It is a convenient reference, since it is fairly constant at all latitudes, in contrast with degrees of longitude which vary from 60 NM at the equator to zero at the poles. Thus, the 1 NM is equivalent to 1852 meter.

1609.344

The statute mile was defined by an English Act of Parliament (hence the name) in 1592, during the reign of Queen Elizabeth I as being 1,760 yards (5,280 feet, about 1609 metres). For surveying, the statute mile is divided into eight furlongs; each furlong is ten chains; each chain is four rods (also known as poles or perches); and each rod is 25 links. This makes the rod equal to 5 yards or 16 feet in both Imperial and U.S. usage.

0.02957

1 fluid ounce in US is equivalent to 0.02957 litter. This is based on the earlier definition of one gallon equaling 231 cubic inches. This measurement at first glance does not seem to have any tie to mass, however it is believed to have come from a previous measure of a gallon as being 224 cubic inches (just 7 cubic inches less, both numbers being multiples of 7) which was used because it was the exact volume of 8 pounds of wine.

4.40488

1 dry gallon, lesser used in 3 "gallon" unit, is equivalent to 4.40488 liter. This is one-eighth of a US Winchester bushel of 2150.42 cubic inches, thus it is equal to exactly 268.8025 cubic inches.

4.54609

1 imperial gallon is equivalent to 4.54609 litter. This definition is used in some Commonwealth countries and Ireland, and is based on the volume of 10 pounds of water at 62 °F. The imperial fluid ounce is defined as 1 160 of an imperial gallon. On 1 January 2000, it ceased to be a legal unit of measure within the United Kingdom for economic, health, safety or administrative purposes.

3.78541

1 gallon in US is equivalent to 3.78541 litter. This is about 0.133680555 cubic feet. This is the most common definition of a gallon in the United States. The US fluid ounce is defined as 1 128 of a US gallon.

6.58211899 x 10^-16

Dirac's constant is defined as the Planck constant divided with 2π, and the value is 6.58211899 x 10^-16.
The spin of electron is half of this value.

5.670440 x 10^-8

Stefan-Boltzmann constant is used in the Stefan-Boltzmann law; the energy of electromagnetic wave. The formulae is defined as I, the energy of electromagnetic wave, is equivalent to T, the thermodynamic temperature, by four times and multiplied with σ, the Stefan-Boltzmann constant.

6.67428 x 10^-11

According to the law of universal gravitation, the attractive force (F) between two bodies is proportional to the product of their masses (m1 and m2), and inversely proportional to the square of the distance (r) between them:

F = G x (m1 x m2)/r^2

The constant of proportionality, G, is the gravitational constant.

The gravitational constant is perhaps the most difficult physical constant to measure to high accuracy. In SI units, the 2006 CODATA-recommended value of the gravitational constant is 6.67428 x 10^-11.

376.730313461

The impedance of vacuum is defined as multiplying electric constant by the light speed. The value is 376.730313461...

5.05078324 x 10^-27

The nuclear magneton is the natural unit for expressing magnetic dipole moments of heavy particles such as nucleons and atomic nuclei. On the contrary, the dipole moment of the electron, which is much higher as a consequence of much higher charge-to-mass ratio, is usually expressed in corresponding units of the Bohr magneton.

The value of nuclear magneton is defined as follows;

μN = e / 2 mp = 5.05078324(13)×10−27
J/T

where:

e is the elementary charge,
is the reduced Planck constant,
mp is the proton rest mass.

1.67492716 x 10^-27

The invariant mass of neutron is 1.67492716 x 10^-27.

The neutron is a subatomic particle with no net electric charge and a mass slightly larger than that of a proton. With the exception of hydrogen, nuclei of atoms consist of protons and neutrons, which are therefore collectively referred to as nucleons. The number of protons in a nucleus is the atomic number and defines the type of element the atom forms. The number of neutrons is the neutron number and determines the isotope of an element. For example, the abundant carbon-12 isotope has 6 protons and 6 neutrons, while the very rare radioactive carbon-14 isotope has 6 protons and 8 neutrons.

1.672621637 x 10^-27

The invariant mass of proton is 1.672621637 x 10^-27. Absolutely larger than that of electron.

9.10938215 x 10^-31

The invariant mass of electron is 9.10938215 x 10^-31. The invariant mass is a characteristic of the total energy and momentum of an object or a system of objects that is the same in all frames of reference related by Lorentz transformations.

927.4 x 10^-26

In atomic physics, the Bohr magneton (symbol μB) is a physical constant and the natural unit for expressing an electron magnetic dipole moment. The Bohr magneton is defined in SI units by μB = e / 2me where
e is the elementary charge,
is the reduced Planck constant and
me is the electron rest mass.

8.854187187... x 10^-12

The physical constant ε0, commonly called the electric constant, relates the units for electric charge to mechanical quantities such as length and force.
The value is defined as 1/(c0^2 x μ0), where c0 is the speed of light in vacuum and μ0 is the magnetic constant.

The most common use of this constant is Gauss's law; Φ = Q/ε0.

3.75

Glucose is a ubiquitous fuel in biology. It is used as an energy source in most organisms, from bacteria to humans. Use of glucose may be by either aerobic respiration, anaerobic respiration, or fermentation. Carbohydrates are the human body's key source of energy, through aerobic respiration, providing approximately 3.75 kilocalories of food energy per gram

146

The glucopyranose forms predominate in solution, and are the only forms observed in the solid state. They are crystalline colorless solids, highly soluble in water and acetic acid, poorly soluble in methanol and ethanol. They melt at 146°C, especially α-glucose, and decompose at higher temperatures into carbon and water.