Pound

What Is Pound?

A pound is a unit used to tell how heavy something is. People use it in daily life to measure things like body weight, food, luggage and many other objects. Today, when people say pound in science or everyday use, they almost always mean the international avoirdupois pound, which is exactly linked to the kilogram.

The pound is still popular in a few countries, even though most of the world uses the metric system with kilograms and grams. The symbol for the pound is lb, and the plural is lb or lbs.

Definition

Modern science gives a very clear definition for the avoirdupois pound.

Official definition

One international avoirdupois pound is defined as exactly 0.45359237 kilograms.

This means:

• 1 pound lb equals 0.45359237 kilograms kg
• 1 kilogram kg equals about 2.2046226218 pounds lb

In everyday life, people usually round these numbers:

• 1 pound is about 0.45 kilograms
• 1 kilogram is about 2.2 pounds

Pound as weight and mass

In simple talk, people say weight when they mean how heavy something is, so they say “I weigh 120 pounds”. In physics, a pound can mean:

• a unit of mass, like the kilogram
• or, in some old systems, a unit of force called pound force

In modern everyday use, pound almost always means a unit of mass, not force.

History / Origin

The pound has a very long history that goes back thousands of years.

Roman beginnings

• The word pound comes from the Latin word “libra” which meant a balance or pair of scales.
• Libra is also why the symbol for pound is lb, from the first letters of the Latin word.
• The Romans used the libra as a unit of weight, and later European systems grew from this idea.

Medieval Europe

• After the Roman Empire, many regions in Europe built their own versions of the pound.
• There were several types, such as the merchants pound, the tower pound and others, which did not all have the same size.
• In England, different pounds were used for different trades, which caused confusion for buyers and sellers.

Avoirdupois pound

• Over time, a system called avoirdupois became the main system for everyday goods.
• The avoirdupois pound was divided into 16 ounces and used for things like food, wool and many other items.
• This is the pound we still use in daily life today.

Modern standard

• In the nineteenth and twentieth centuries, scientists worked to connect old units to the new metric system.
• They agreed that 1 avoirdupois pound would be exactly 0.45359237 kilograms.
• This fixed link to the kilogram made the pound stable and easy to use in science and trade.

Symbol & Abbreviation

The pound has easy symbols that you will often see on packages, scales and recipes.

• Main symbol: lb
• Plural form: lb or lbs both are used in practice
• Spelling: pound for singular, pounds for plural in normal writing

Examples in writing:

• “The box weighs 10 lb” or “The box weighs 10 lbs”
• “I bought 2 lb of apples”

Do not confuse the weight unit pound with the money unit pound, which uses symbols like £ for British pounds. They are different units, even though they share the same word.

Current Use Around the World

Most countries use the metric system, but the pound is still important in some places and in some fields.

Main places that use the pound

• United States: The pound is the main unit for body weight, many foods, sports and everyday items. People say things like “150 pounds” or “a 5 pound bag of flour”.
• United Kingdom: The UK is mostly metric for official use, but people still use stones and pounds for body weight and pounds for some foods and everyday talk.
• Canada: Canada is officially metric, but pounds and ounces are still used in many shops, in cooking and in daily speaking, especially for body weight.
• Other countries: Some other countries with strong links to the US or UK sometimes use pounds in trade or in older documents, but kilograms are more common.

Fields where pound is common

• Health and fitness: Body weight is often given in pounds, for example 120 lb.
• Food and cooking: Recipes and store labels may say 1 lb of meat or 3 lb of potatoes.
• Sports: In sports like boxing or wrestling, fighters are placed into weight classes given in pounds, such as 135 lb or 200 lb.
• Engineering and industry: In the United States, many engineering areas still use pounds and related units, such as pounds per square inch psi for pressure.

Even in countries that mostly use kilograms, people sometimes know their body weight in both kilograms and pounds, because many international charts and tools use pounds.

Example Conversions

Here are some helpful conversion examples between pounds and other units. These are based on the exact link 1 lb equals 0.45359237 kg.

Pounds to kilograms

• 1 lb equals 0.45359237 kg
• 2 lb equals 0.90718474 kg about 0.91 kg
• 5 lb equals 2.26796185 kg about 2.27 kg
• 10 lb equals 4.5359237 kg about 4.54 kg
• 100 lb equals 45.359237 kg about 45.36 kg

Kilograms to pounds

• 1 kg equals about 2.20462 lb
• 2 kg equals about 4.40925 lb
• 5 kg equals about 11.0231 lb
• 10 kg equals about 22.0462 lb
• 50 kg equals about 110.231 lb

Pounds to ounces

In the avoirdupois system, 1 pound equals 16 ounces oz.

• 1 lb equals 16 oz
• 0.5 lb equals 8 oz
• 2 lb equals 32 oz
• 5 lb equals 80 oz

Pounds to grams

Because 1 kg equals 1000 g, we can also convert directly to grams.

• 1 lb equals 453.59237 g about 454 g
• 0.5 lb equals about 226.8 g
• 2 lb equals about 907.2 g
• 10 lb equals about 4536 g

Pounds to stones mainly used in the UK

• 1 stone st equals 14 lb
• 8 st equals 112 lb
• 10 st equals 140 lb
• 12 st equals 168 lb

Pounds to tons

• 1 short ton US equals 2000 lb
• 1 long ton UK equals 2240 lb
• 1 metric ton tonne equals 1000 kg which is about 2204.62 lb

Related Units

The pound belongs to a family of units used to measure mass or weight. Here are the most closely related ones.

• Ounce oz: Smaller unit in the same system. 1 lb equals 16 ounces.
• Stone st: Used mainly for human body weight in the UK. 1 stone equals 14 pounds.
• Ton: Very large unit for heavy loads. Short ton and long ton are based on pounds. The metric ton is based on kilograms.
• Kilogram kg: Main metric unit of mass. 1 lb equals 0.45359237 kg exactly.
• Gram g: Smaller metric unit. 1000 g equals 1 kg, so 1 lb is about 454 g.
• Pound force lbf: In older physics and engineering systems, this was a unit of force related to the pound of mass. Today, the newton is the standard force unit.
• Troy pound rare today: Older type of pound used for precious metals in some places. It is different from the avoirdupois pound and is not used much anymore.

FAQs

What is a pound in simple words?

A pound is a unit used to tell how heavy something is. In most everyday cases, 1 pound is a little less than half a kilogram.

How many kilograms are in 1 pound?

Exactly 1 pound equals 0.45359237 kilograms. For quick math in your head, you can remember that 1 pound is about 0.45 kilograms.

How many pounds are in 1 kilogram?

1 kilogram equals about 2.20462 pounds. A simple rule to remember is that 1 kilogram is a bit more than 2.2 pounds.

How many ounces are in a pound?

In the common avoirdupois system, 1 pound equals 16 ounces. So to go from pounds to ounces, you multiply by 16.

Is the pound a metric unit?

No. The pound is not part of the metric system. The metric system mainly uses grams and kilograms. But the pound is exactly linked to the kilogram so they can work together.

Do all countries use pounds?

No. Most countries use kilograms instead. Pounds are mainly used in the United States, in daily life in the United Kingdom and in some other English speaking places.

What is the difference between lb and lbs?

Both lb and lbs are used as abbreviations for pounds. lb comes from the Latin word libra. Many style guides prefer lb for both singular and plural.

Is the weight pound the same as the money pound?

No. The weight pound measures how heavy something is and uses the symbol lb. The money pound is a currency used in some countries and often uses the symbol £.

What is a troy pound?

A troy pound is an old type of pound used mainly for precious metals in some places. It has 12 troy ounces, not 16, and is different from the everyday avoirdupois pound.

Why do scientists prefer kilograms instead of pounds?

Scientists prefer kilograms because they are part of the metric system, which is used worldwide and is easier for careful math. But they still know the exact link between kilograms and pounds so they can convert when needed.