Weight Converter: Kilograms, Pounds, Ounces, Stones & Tons

Convert weight and mass measurements between metric, US customary, Imperial, scientific and specialist units. Use this weight converter for luggage, body weight, recipes, parcels, freight, manufacturing and laboratory measurements.

For the most common international calculations, use the kilograms to pounds converter or convert in the opposite direction with the pounds to kilograms converter.

Common Weight and Mass Units

Everyday measurements usually use kilograms, grams, pounds or ounces. Freight and industrial materials may be measured in tonnes or tons, while precious metals, gemstones and scientific samples require more specialised units.

Kilogram (kg): The SI base unit of mass, commonly used for body weight, luggage, food, parcels and commercial goods.
Gram (g): A metric unit equal to 0.001 kilogram. It is widely used for ingredients, packaged food, laboratory samples and small objects.
Milligram (mg): A metric unit equal to 0.001 gram, commonly used for medicines, supplements, chemicals and small scientific samples.
Microgram (µg): A unit equal to one-millionth of a gram, used for vitamins, medications, pollutants and laboratory measurements.
Metric tonne (t): A metric unit equal to 1,000 kilograms, used for freight, vehicles, agricultural products and industrial materials.
Pound (lb): An avoirdupois unit equal to exactly 0.45359237 kilograms. Pounds are widely used for body weight, luggage, food and parcels in the United States.
Ounce (oz): One-sixteenth of an avoirdupois pound, commonly used for food portions, postal items and relatively light objects. One avoirdupois ounce is approximately 28.3495 grams.
Stone (st): A unit equal to 14 pounds and still commonly used for personal body weight in the United Kingdom and Ireland.
US short ton: A unit equal to 2,000 pounds, or approximately 907.185 kilograms. It is used for freight, machinery and bulk materials in the United States.
Imperial long ton: A unit equal to 2,240 pounds, or approximately 1,016.047 kilograms. It appears in some British, maritime and historical measurements.
Hundredweight (cwt): A unit equal to 100 pounds in the US system but 112 pounds in the Imperial system. The intended definition must be identified before conversion.
Troy ounce (oz t): A unit equal to exactly 31.1034768 grams and used primarily for precious metals such as gold, silver, platinum and palladium.
Carat (ct): A unit equal to exactly 200 milligrams, used to state the mass of diamonds and other gemstones.
Grain (gr): A unit equal to exactly 64.79891 milligrams. It is still encountered in ammunition, archery and some traditional pharmaceutical measurements.
Unified atomic mass unit (u): An extremely small unit used to describe the masses of atoms, molecules and subatomic particles. It is also known as the dalton.

In everyday language, weight and mass are often used interchangeably. Scientifically, mass describes an object’s resistance to acceleration, while weight is the force exerted on that mass by gravity. General-purpose converters commonly treat kilograms and pounds as mass units.

When Is Weight Conversion Useful?

Weight conversion is useful when checking airline baggage limits, recording body weight, adapting recipes, comparing food packages or preparing an international parcel. It also supports logistics, manufacturing, agriculture, engineering, laboratory work and commercial trade.

Reliable conversion begins with the complete unit name. An ordinary ounce differs from a troy ounce, while a short ton, long ton and metric tonne represent three different quantities.

Real-Life Stories Behind Weight and Mass Conversion

People traded grain, metals, cloth and other goods by weight long before countries agreed on common measurement standards. Names such as pound, ounce, stone and ton were reused in different places, but their values were not always identical. Modern definitions now allow these units to be converted consistently into kilograms and grams.

A 70 kg Astronaut Does Not Lose Mass on the Moon

Everyday language often treats mass and weight as the same thing, but physics distinguishes between them. Mass describes an object’s inertia and is measured in kilograms. Weight is the force created when gravity acts on that mass, so its scientific unit is the newton.

Weight can be calculated using:

Weight = mass × gravitational acceleration

Near Earth’s surface, a person with a mass of 70 kg has an approximate gravitational weight of:

70 kg × 9.81 m/s² ≈ 687 N

The Moon’s surface gravity is approximately 1.62 m/s². The same person would therefore have a lunar weight of:

70 kg × 1.62 m/s² ≈ 113 N

The astronaut still has a mass of 70 kg because the amount of matter and the body’s inertia have not changed. Only the gravitational force is smaller. This weaker force helps explain the bounding movements visible in footage of astronauts walking on the Moon.

NIST explains that the kilogram measures mass while scientific weight is a force . Lunar gravity data are available through NASA’s Moon Fact Sheet .

Why a Suitcase Can Be 23 kg and 50.7 lb

International travel provides a common reason to convert kilograms and pounds. An airline might publish a checked-baggage allowance of 23 kg, while a passenger’s home scale displays pounds. Both measurements can describe the same suitcase:

23 kg ≈ 50.71 lb

The relationship is stable because the international avoirdupois pound is defined as exactly 0.45359237 kilograms. Converting the displayed number does not make the suitcase heavier or lighter; it expresses the same mass using another unit.

A traveller can calculate the value with the kg to lb converter. If the baggage scale displays pounds but the booking gives a kilogram limit, the lb to kg converter performs the reverse calculation.

Rounded airline limits require care. Although 23 kg is sometimes shown beside 50 lb, they are not exact equivalents:

23 kg ≈ 50.71 lb
50 lb ≈ 22.68 kg

Travellers should follow the exact unit and limit on their booking. Leaving a small margin can also help account for differences between a household luggage scale and the airport’s equipment.

NIST publishes the official relationship in its mass and force conversion tables .

An Ounce of Gold Is Not the Same as an Ounce of Food

The word ounce can identify two different mass units. Food, parcels and ordinary household goods normally use the avoirdupois ounce, while gold, silver and other precious metals are commonly measured in troy ounces.

1 avoirdupois ounce ≈ 28.3495 g
1 troy ounce = 31.1034768 g

A troy ounce is about 9.7% heavier than an avoirdupois ounce. The distinction matters when comparing the price or mass of precious metals with an ordinary product.

The pound systems introduce another difference. An avoirdupois pound contains 16 avoirdupois ounces, while a troy pound historically contains 12 troy ounces. The complete unit name is therefore more informative than the word “ounce” by itself.

A Ton Can Mean Three Different Quantities

Large cargoes are often described in tons, but the word does not identify one universal mass. Three definitions are commonly encountered:

US short ton = 2,000 lb ≈ 907.185 kg
Imperial long ton = 2,240 lb ≈ 1,016.047 kg
Metric tonne = 1,000 kg ≈ 2,204.623 lb

The difference becomes substantial when calculating freight, machinery, coal or construction materials. A shipment described as 100 tons could vary by more than ten metric tonnes depending on which definition was intended.

In international documents, writing short ton, long ton or metric tonne removes the ambiguity. A converter should likewise require the specific unit rather than assume every ton has the same value.

Where Weight and Mass Converters Are Used Today

Kilograms and pounds are compared when packing luggage, recording body weight and shipping parcels. Grams and ounces appear in recipes and food packaging, while milligrams and micrograms are used for medicines, nutrients and laboratory samples.

Farms, factories and freight companies work with kilograms, metric tonnes and several definitions of the ton. Jewellers and commodity markets use carats and troy ounces, while scientific work can involve atomic mass units.

Before converting, identify the complete source unit and preserve an appropriate level of precision. The numerical value may change, but a correct unit conversion always represents the same underlying mass.

Weight Converter