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Algebraic Steps / Dimensional Analysis Formula
0.453592 kg
1 lb

Conversion to common lengths

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Algebraic Steps / Dimensional Analysis Formula
1 lb
0.453592 kg

Conversion to common lengths


Pounds and kilograms – the difference

The curiosity of humanity has led it to advance by leaps and bounds compared to other beings in the animal kingdom.

Pounds to Kilograms

Because of that humankind had many discoveries and scientific advances that have led us to our current technological achievements.

Natural phenomena such as light, heat, sound, electricity and gravity can be described in detail thanks to all the scientific achievements in the past.

History of the “pound” as a unit of weight

In order to carry out their activities as accurately as possible, humans had to officially declare how to measure the world around them.

The word pound comes from the Latin “Libra” and means “balance”. We can take the word “balance” as a reference: In Latin it is translated with “aequilibrare”. The term “aequus” (equal to) added to “libra” (scale) would result in the translation “make equal to the scale”.

A good example was when building a bridge. The ancient Romans had to deduce the approximate weight that a bridge could withstand based on its length and the mass of people, animals and merchandise that would pass through it. To measure the length of large objects, the Romans invented the “Roman foot” which is equivalent to 29.6 centimeters (cm) today.

As its name implies, the “Roman foot” was the approximate length of a common person’s right foot (the left foot was considered bad luck in ancient Rome). For weight, the Romans devised a unit of mass called the “Roman pound” that is currently equivalent to 273 grams (g).

Libra - Pounds to Kilograms

The “Libra avoirdupois” (in English “Pound avoirdupois”) belongs to the so-called “Anglo-Saxon system” or “imperial system” of measures. It is commonly called simply “pound” or “pounds (plural)” in English. In this text, when we refer to the pound, we will be referring to the “avoirdupois pound”. This system has its origin in the United Kingdom and is a derivative of the measurement systems used by the ancient Romans. As it was adapted by the British colonies as the British Empire expanded around the world, the system was also called the “imperial system”.

This system has the following basic units:

  • Inches (in), feet (ft), yards (yd), and miles (mi) as units of length.
  • Acres (ac) as a unit of area or surface.
  • Ounces and gallons as units of volume for liquids.
  • Cubic inches, cubic feet and cubic yards to measure volumes of solids.
  • Pounds (lb/lbs) and ounces (oz) as units for measuring the mass of bodies for example.

Different systems of measurement of the pound

However, these measurements proved not always to be completely accurate. After the fall of the Roman Empire, many regions of Europe adapted their own measurement of mass (pound) which would make it even more difficult to have a unit of mass with which to accurately weigh any object.
We can briefly review several historical “pounds” that have been defined over the years and are currently obsolete:

  • The Anglo-Saxon pharmaceutic pound (pound apothecary): Used in pharmacies and pharmacology. It is currently equivalent to 373.2417 grams.
  • The Castilian pound: It was used by the Spanish empire and its overseas colonies. It currently equals 469.093 grams.
  • The Castilian Pharmaceutical Pound: Used in Spanish pharmacies and pharmacology. It currently equals 345.06975 grams.
  • The Catalan pound: Used in the Catalan territories. It is currently equivalent to 400 grams.
  • The Zaragozan pound: Used in the Zaragoza territories. It is currently equivalent to 350 grams.
  • The Guipúzcoana pound: Used in the territories of Guipúzcoa. It currently equals 492 grams.
  • The Neapolitan pound: Belonging to the ancient “Kingdom of Naples”. It currently equals 320.759 grams.

Relationship between “pounds” and “kilograms”

Currently the units of the “international system” and the “imperial system” coexist to this day. Most of the countries of the world use the units of the “international system”. An important part of this system are the units of measurement that are used in science. In the areas of knowledge related to physics, a special abbreviation is used with the acronym “MKS” which means “Meters-Kilograms-Seconds“.

However, the United States of America, Liberia and Burma officially use the “Imperial System”. The United Kingdom has officially used the “International System” since 1973, because it became part of the European Economic Community.

In September 1999, the National Aeronautics and Space Administration (NASA) carried out a mission to the planet Mars called “Mars Climate“.

This project consisted of placing a probe in orbit around Mars to study its atmosphere and surface. The probe was a joint project between two large propulsion laboratories; one of the laboratories was the “Jet Propulsion Laboratory” in Pasadena, California, which used units of the “International System” (meters and kilograms) for all their calculations.

However, the other laboratory, belonging to the company “Lockheed Martin Astronautics” located in Denver, Colorado used the “Imperial System” for its calculations (feet and pounds). As a result, after starting the mission and finding itself in an orbit position with Mars, the probe did not have a correct reading of its position, weight, and acceleration, which made it impossible for it to enter the planet’s orbit correctly. The angle of entry was wrong and the probe ended by impacting on the surface of Mars. The engineering teams had completely forgotten to transform the units from one system to another, so that the probe had a unit reading in all its sensors, which would have guaranteed the success of the mission.

The anecdote continues to be one of the most shameful cases in the history of the exploration of our solar system and a clear example of the conflict that is part of the relationship between the different measurement systems.

Precisely the problem between both systems is their conflict. There is no 1: 1 (one to one) relationship between the units of both systems (only the time in seconds is assimilated with the same magnitude between both systems).

We cannot establish a relation of a “pound” = “kilogram”. Even more complicated is that the relationship between the two units is not even equivalent in whole numbers.

The differences between both units of mass is very remarkable.

One (1) pound is approximately a little less than half the weight represented by a kilogram (½ Kg).

Taking this comparison, we can say that one (1) kilogram contains a little more than the value of weight represented in the mass of two (2) pounds.

However, it is necessary to define precisely the figures associated with the weight of both units.

To measure the mass of an object, the “Imperial System” uses the pound (lb or lbs). We can say that a pound equals 0.453592 kilograms in the “International System”.

Similarly, we can say that a kilogram is equivalent to 2.20462 pounds.

Converting from “pounds” of weight to “kilograms”

Formula to convert from “pounds” to “kilograms”:

1 kilogram (kg) = 2.20462 pounds (lbs)

Suppose you are going to buy a basket of apples.

The store manager informs you that the apples in the basket weigh approximately 30 pounds, however you need to know the weight in kilograms to follow a recipe.

You would need to convert or translate that weight in pounds to its equivalent weight in kilograms. For this calculation we will take the following relationship:

2.2 pounds (lbs) equals 1 kilogram (kg)

Therefore, we would have to divide the weight of the basket (30 lbs) by the ratio we have established from pounds to kilograms (2.2 lbs).

The result would be approximately 13.6363 kilograms (kg). If we “round” or “approximate” their decimals, we would obtain approximately 14 kilograms of apples.

This means that 30 Pounds (lb) of apples, roughly equal to 14 kilograms (kg)

Facilitation of conversion calculation

The present cases of conversion between pounds of weight and kilograms can be extremely confusing, even using mathematical formulas. You may wonder how do I know when to divide by kilograms or pounds to convert to the unit I want?

The answer is supported by mathematics.

Taking the example of apples: If you want to convert an object’s weight in pounds to kilograms, you need to divide by the respective value of pounds that equals one kilogram (2.20462 Pounds).

We can establish the following relationship: pounds x kilograms / (2.20462 pounds) = weight in kilograms.

Otherwise, if you want to convert an object’s weight in kilograms to pounds, you must use the mathematical conversion formula. You must divide by the kilograms value that one pound equals (0.453592 kilograms). The mathematical formula can be defined in a practical way as:

kilograms x pounds / (0.453592 kilograms) = weight in pounds

In mathematical terms: the divisor of the equation will always be eliminated with its pair in the dividend (If you divide by kilograms (kg), the result will be reflected in pounds (lb); if you divide by pounds (lb), the result will be reflected in kilograms (kg).

Practical examples using “pounds” and “kilograms”

Perhaps you may wonder: What practical examples can currently be applied both to pounds of weight and to kilograms? Why are these conversions necessary? Here are several examples of the use of both systems:

The kilogram is currently used in the food industries: vegetables, fruits and cereals. Additionally, personal hygiene products such as cotton and paper. Beauty products, such as makeup powder, have their weight expressed in grams (g).
The pound (lb) of weight is mostly related to the weight of precious metals as we have already indicated previously. The weight of gold, silver and tin are mostly traded in pounds (lb). It may also be common for the load capacity of heavy machinery such as tractors or forklifts to be expressed in pounds.

The pound is also related to products produced in the United States. This implies that in that country, you can find pounds in products such as: food, textiles, shoes and clothing to mention a few specific examples.

Study of the “pound” and its derived units:

For its part, the pound of weight (lb) is made up of the units: grain (gr), drachma (dr), and ounce (oz). Of the previous three units, the most used commercially is the ounce (oz). One pound contains sixteen ounces (1 pound = 16 oz). There are several units of mass greater than the pound that belong to the same “Imperial System”. We define them below:

The “quintal”, the “quarter” and the “ton” have different values ​​according to the country in which they are used: for the United States of America (United States) the ending “short” is used, while for the units for the United Kingdom, the ending “long” is used on a commercial level. The most commonly used units are the ounce, the quintal and the ton.
  • The “grain” (gr) equivalent to 0.000142857 pounds (1 gr = 0.000142857 lb)
  • The “drachma” (dr) equivalent to 0.00390625 pounds (1 dr = 0.00390625 lb)
  • The “ounce” (oz) equivalent to 0.0625 lb (1 oz = 0.0625 lb)
  • The “stone” (st) equals fourteen pounds (1 st = 14 lb).
  • The “arroba” is equivalent to 25 pounds (1 arroba = 25 pounds).

  • The “short quintal” (US ctw) equivalent to one hundred pounds (1 US ctw = 100 lb)
  • The “long quintal” (UK ctw) equivalent to 112 pounds (1 UK ctw = 4 = 112 pounds)
  • The “short quarter” (US qtr) equivalent to 20 arrobas or 500 pounds (1 US qtr = 20 arrobas = 500 lb)
  • The “long quarter” (UK qtr) equivalent to 5 long quintals or 560 pounds (1 UK qtr = 5 UK ctw = 560 lb)
  • The “short ton” (US ton) equivalent to 4 short quarts (4 US qtr) or 2000 pounds (1 US ton = 4 US qtr = 2000 lb)

  • The “long ton” (UK ton) equivalent to 4 long quarts (4 UK qtr) or 2,240 pounds (1 UK ton = 4 UK qtr = 2,240 lb)

In order to make correct use of the mass units of the imperial system, it is necessary to know how to correctly carry out the conversions between their units.

In this case, we will take the most commercial units used today, which are: the ounce, the stone, the quintal and the ton.

Next we will develop a list of equivalences, based on the previous paragraph, in which we will develop the equivalence of these units with the pound:

  • 1 pound = 16 ounces (oz). Turn (1 oz = 0.0625 lb)
  • 1 stone = 14 pounds (lb). Turn (1 lb = 0.0714 lb)
  • 1 short quintal (US ctw) = 100 pounds (lb). Turn (1 lb = 0.01 US ctw)
  • 1 long quintal (UK ctw) = 112 pounds (lb). In turn (1 lb = 0.0089 UK ctw)
  • 1 short ton (US ton) = 2000 pounds (lb). In turn (1 lb = 0.0005 US ton)
  • 1 long ton (UK ton) = 2,240 pounds (lb). In turn (1 lb = 0.0004464 UK ton)

Examples of comparison with everyday objects

We can associate the weights with common objects of our day to day.

A good example is the food we buy at the market. Did you know that an apple weighs approximately 250 grams? This would mean that if you buy a kilogram of fresh apples, you would be buying approximately four (4) apples.

In the same way, if you buy two apples that weigh 250 grams each, you would be buying a little more than a pound (500 grams) of weight in apples: 1 Pound (lb) = 453,592 grams (g).

Another example we can take when buying liquids.

A liter of drinking water is equivalent to a kilogram of weight and as we have seen previously, a kilogram is equivalent to 2.20462 pounds (1 liter = 1 Kg = 2.20462 lb).

Milk, due to its density, the product of its chemical composition, has an approximate weight of 1.030 kilograms (kg) per liter.

A curious fact is that in the Republic of Colombia in South America, the “pound” is popularly called the weight equivalent to 500 grams (g). However, Colombian law does not allow labeling this weight measurement on any product, because it is incorrect.

Problems between conversions

The conversion between units of mass of different systems is not precise. As we have explained, the relationship between pounds and kilos is not comparable to a linear system or a one-to-one (1: 1) relationship. The result of the conversions between both units always results in magnitudes that contain a large number of decimal places. Let’s look at several examples:

Now if we take these 2.0462 pounds of weight (lb) and transform them back into kilograms (kg) we get a total of 0.9999988107 kilograms (kg). As you can see, the result is not a complete unit (1 Kg), during the conversion we have lost approximately 0.0000011893 kilograms (kg) in the conversion (0.00011893% of its original value).

Certainly the lost percentage is not much, but when calculating large figures it can be very damaging.

Let’s take an example, we want to convert 3000 kilograms (kg) of weight to pounds (lb). If we do the calculations explained above for the conversion between kilograms (kg) and pounds (lb) we obtain that 3000 kilograms is equivalent to 6613.8732 pounds. Now, let’s transform these 6613.8732 pounds of weight back into kilograms, what would be the result? Well, these 6613.8732 pounds now equal 3,000.006 kilograms.

Only by converting the same weight between different units, we have added 0.006 kilograms (0.6 grams = 600 milligrams) to the original weight.

Conversion between units can never be completely accurate. The present example is a good reason why it is advisable to perform mathematical calculations of any type with a minimum of four decimal places, as we normally do with geometric and radial calculations based on the number “Pi” Π = 3.1415926 (the number is almost always rounded to a value of 3.1416)
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