The Complete Guide to Weight and Mass Conversion — Kilograms, Pounds, Ounces and More

Weight and mass conversion is one of the most frequently needed calculations in everyday life. Whether you are following a recipe, tracking your fitness progress, shipping a package internationally, understanding a medical prescription, or working in engineering — the ability to convert accurately between kilograms, pounds, ounces, grams, and other units of mass is an essential skill. This complete guide explains the difference between mass and weight, covers every major unit of mass used around the world, and gives you the exact conversion factors and worked examples you need.

Mass vs Weight — An Important Distinction

Before diving into conversions it is worth understanding the difference between mass and weight, because these terms are used interchangeably in everyday life but have distinct meanings in science and engineering.

Mass is the amount of matter contained in an object. It is an intrinsic property that does not change regardless of where the object is located. A person with a mass of 70 kilograms has a mass of 70 kilograms whether they are standing on Earth, floating on the International Space Station, or standing on the Moon.

Weight is the force exerted on an object by gravity. It depends on both the object’s mass and the local gravitational field strength. Weight is measured in Newtons (N) in the SI system. On Earth, a 70 kg person weighs approximately 686 Newtons (70 × 9.81 m/s²). On the Moon, where gravity is about one sixth of Earth’s, the same person would weigh only about 114 Newtons — but their mass remains 70 kg.

In everyday life when we say someone weighs 70 kg we technically mean their mass is 70 kg. The scales in your bathroom measure mass, not force. This distinction rarely matters for everyday conversions but is important in physics, engineering, and space science.

The Major Units of Mass

Kilogram (kg)

The kilogram is the SI base unit of mass and is the standard unit of mass used in science, medicine, engineering, and everyday life in most countries worldwide. One kilogram is defined since 2019 by fixing the numerical value of Planck’s constant — a quantum physics constant — making it the most precisely defined unit of mass in history.

Practical reference points:

• 1 kg — a litre of water, a small bag of sugar, a typical hardback book
• 5 kg — a bag of flour, a newborn baby, a large bag of potatoes
• 70 kg — average adult human body mass
• 1,000 kg — one metric tonne, approximately the mass of a small car

Gram (g)

One gram is one thousandth of a kilogram. It is used for smaller masses in cooking, medicine, chemistry, and everyday weighing.

Practical reference points:

• 1 g — a paperclip, a small sugar cube, a US dollar bill
• 5 g — a teaspoon of water, a standard pen cap
• 100 g — a small apple, a deck of cards
• 500 g — a standard block of butter

Milligram (mg)

One milligram is one thousandth of a gram or one millionth of a kilogram. Milligrams are used in medicine for drug dosing, in nutrition for vitamins and minerals, and in chemistry for precise measurements.

Practical reference points:

• 1 mg — a grain of salt, a small grain of sand
• 500 mg — a standard paracetamol tablet
• 1,000 mg — 1 gram

Pound (lb)

The pound is the primary unit of mass in the imperial system and is used for everyday weight measurement in the United States and partially in the United Kingdom. The legal definition of one pound is exactly 0.45359237 kilograms — a definition that has been internationally agreed since 1959.

Practical reference points:

• 1 lb — approximately 454 grams, roughly the weight of a loaf of bread
• 10 lb — approximately 4.5 kg, a large bag of potatoes
• 154 lb — approximately 70 kg, average adult
• 2,000 lb — one US short ton

Ounce (oz)

One ounce is one sixteenth of a pound. Ounces are used in cooking (particularly in American recipes), precious metals trading, and postal weights.

• 1 oz = 28.3495 grams
• 16 oz = 1 pound

Note: there is also a troy ounce used for precious metals (gold, silver, platinum) which is slightly heavier than the standard (avoirdupois) ounce. 1 troy ounce = 31.1035 grams, compared to 1 standard ounce = 28.3495 grams.

Stone (st)

The stone is a unit of mass used almost exclusively in the United Kingdom and Ireland for expressing human body weight. It is not used in the United States or most other countries.

• 1 stone = 14 pounds = 6.35029 kg
• A person weighing 11 stone in the UK weighs 154 pounds or approximately 70 kg

Metric Tonne (t)

One metric tonne equals 1,000 kilograms. It is the standard large unit of mass in the SI system used for vehicles, cargo, construction materials, and industrial quantities.

• 1 tonne = 1,000 kg = 2,204.6 lbs
• A standard car weighs approximately 1.3–1.8 tonnes
• A shipping container can hold up to approximately 28 tonnes of cargo

US Short Ton

The US short ton equals 2,000 pounds or approximately 907 kilograms. It is used in the United States for large quantities of goods, materials, and cargo.

• 1 US short ton = 2,000 lb = 907.185 kg

UK Long Ton (Imperial Ton)

The UK long ton equals 2,240 pounds or approximately 1,016 kilograms. It is the traditional British ton and is still used in some contexts in the UK and in maritime shipping.

• 1 long ton = 2,240 lb = 1,016.05 kg

The existence of three different “tons” — metric tonne (1,000 kg), US short ton (907 kg), and UK long ton (1,016 kg) — is a frequent source of confusion in international trade and engineering. Always clarify which ton is being used in any commercial or technical context.

Complete Mass Conversion Table

Kilograms to Other Units

Kilograms	Grams	Pounds	Ounces	Stone	Metric Tonnes
0.1 kg	100 g	0.220 lb	3.527 oz	0.0157 st	0.0001 t
0.5 kg	500 g	1.102 lb	17.637 oz	0.0787 st	0.0005 t
1 kg	1,000 g	2.205 lb	35.274 oz	0.1575 st	0.001 t
5 kg	5,000 g	11.023 lb	176.37 oz	0.787 st	0.005 t
10 kg	10,000 g	22.046 lb	352.74 oz	1.575 st	0.01 t
50 kg	50,000 g	110.23 lb	1,763.7 oz	7.874 st	0.05 t
70 kg	70,000 g	154.32 lb	2,469.1 oz	11.023 st	0.07 t
100 kg	100,000 g	220.46 lb	3,527.4 oz	15.747 st	0.1 t
1,000 kg	1,000,000 g	2,204.6 lb	35,274 oz	157.47 st	1 t

Pounds to Other Units

Pounds	Kilograms	Grams	Ounces	Stone
1 lb	0.4536 kg	453.6 g	16 oz	0.0714 st
5 lb	2.268 kg	2,268 g	80 oz	0.357 st
10 lb	4.536 kg	4,536 g	160 oz	0.714 st
50 lb	22.68 kg	22,680 g	800 oz	3.571 st
100 lb	45.36 kg	45,360 g	1,600 oz	7.143 st
150 lb	68.04 kg	68,040 g	2,400 oz	10.714 st
200 lb	90.72 kg	90,720 g	3,200 oz	14.286 st

Body Weight Reference Table

This table is commonly needed for medical, fitness, and travel contexts:

kg	lbs	Stone & lbs
45 kg	99.2 lb	7 st 1 lb
50 kg	110.2 lb	7 st 12 lb
55 kg	121.3 lb	8 st 9 lb
60 kg	132.3 lb	9 st 6 lb
65 kg	143.3 lb	10 st 3 lb
70 kg	154.3 lb	11 st 0 lb
75 kg	165.3 lb	11 st 11 lb
80 kg	176.4 lb	12 st 8 lb
85 kg	187.4 lb	13 st 5 lb
90 kg	198.4 lb	14 st 2 lb
95 kg	209.4 lb	14 st 13 lb
100 kg	220.5 lb	15 st 10 lb
110 kg	242.5 lb	17 st 4 lb
120 kg	264.6 lb	18 st 13 lb

Key Conversion Factors

From	To	Multiply by
Kilograms	Pounds	2.20462
Pounds	Kilograms	0.453592
Kilograms	Grams	1,000
Grams	Kilograms	0.001
Grams	Ounces	0.035274
Ounces	Grams	28.3495
Pounds	Ounces	16
Ounces	Pounds	0.0625
Stone	Kilograms	6.35029
Kilograms	Stone	0.157473
Stone	Pounds	14
Pounds	Stone	0.071429
Metric tonnes	Kilograms	1,000
Kilograms	Metric tonnes	0.001
US short tons	Kilograms	907.185
UK long tons	Kilograms	1,016.05
Metric tonnes	US short tons	1.10231
Metric tonnes	UK long tons	0.984207

Step-by-Step Worked Examples

Example 1 — Converting 75 kg to Pounds

75 kg × 2.20462 = 165.35 lbs

Example 2 — Converting 180 lbs to Kilograms

180 lb × 0.453592 = 81.65 kg

Example 3 — Converting 11 Stone 5 lbs to Kilograms

Step 1 — Convert stone to pounds: 11 × 14 = 154 lbs Step 2 — Add remaining pounds: 154 + 5 = 159 lbs total Step 3 — Convert to kg: 159 × 0.453592 = 72.12 kg

Example 4 — Converting 500 grams to Ounces

500 g × 0.035274 = 17.637 oz

Example 5 — Converting 3.5 Metric Tonnes to Pounds

Step 1 — Convert to kg: 3.5 × 1,000 = 3,500 kg Step 2 — Convert to lbs: 3,500 × 2.20462 = 7,716.2 lbs

Example 6 — Converting 2.5 lbs to Grams (for cooking)

Step 1 — Convert to kg: 2.5 × 0.453592 = 1.134 kg Step 2 — Convert to grams: 1.134 × 1,000 = 1,134 grams

Or directly: 2.5 × 453.592 = 1,134 grams

Mass Conversion in Different Contexts

Cooking and Baking

Cooking is one of the most common everyday contexts for mass conversion. American recipes typically specify ingredients in ounces and pounds, while European, Australian, and most other international recipes use grams and kilograms.

Common cooking conversions:

Imperial	Metric
1 oz	28 g
2 oz	57 g
4 oz (¼ lb)	113 g
8 oz (½ lb)	227 g
12 oz (¾ lb)	340 g
16 oz (1 lb)	454 g
2 lb	907 g
2.2 lb	1 kg

For baking specifically, using weight measurements (grams) is far more accurate than volume measurements (cups) because the density of ingredients like flour varies significantly depending on how it is packed. A cup of loosely sifted flour can weigh as little as 100 grams while a cup of densely packed flour can weigh 160 grams or more — a 60% difference that significantly affects baking results.

Medical and Healthcare

In healthcare, accurate mass measurement is critical for drug dosing, nutritional assessment, and monitoring patient progress. Drug doses are frequently calculated on a milligrams per kilogram (mg/kg) basis — particularly in paediatrics — meaning accurate weight measurement and conversion is directly linked to patient safety.

Medical professionals working internationally need to convert between kg and lbs constantly since patient weights may be recorded in either unit depending on the country. A patient weighing 154 lbs in an American record is 70 kg — an important conversion to make correctly before calculating any weight-based drug dose.

Fitness and Sports

Body weight tracking in fitness typically requires conversion between kg (used in most countries and in scientific research) and lbs (used in the US and common in American fitness content). Weightlifting records and competition standards are almost always stated in kilograms internationally.

Olympic weightlifting weight classes (kg and approximate lbs):

Category	kg	lbs (approx)
Men’s 61 kg	61 kg	134 lbs
Men’s 73 kg	73 kg	161 lbs
Men’s 89 kg	89 kg	196 lbs
Men’s 102 kg	102 kg	225 lbs
Men’s 109 kg	109 kg	240 lbs
Women’s 49 kg	49 kg	108 lbs
Women’s 59 kg	59 kg	130 lbs
Women’s 71 kg	71 kg	157 lbs

Shipping and Logistics

International shipping and freight uses kilograms for mass and metric tonnes for large freight. Volumetric weight (also called dimensional weight) is a concept used by couriers where they charge based on whichever is greater — the actual weight or the volumetric weight calculated from the package dimensions.

DHL/FedEx/UPS volumetric weight formula: Volumetric weight (kg) = Length (cm) × Width (cm) × Height (cm) ÷ 5,000

A package measuring 40 × 30 × 20 cm has a volumetric weight of 40 × 30 × 20 ÷ 5,000 = 4.8 kg. If the actual weight is only 2 kg the courier charges for 4.8 kg.

Engineering and Construction

Engineering uses metric tonnes and kilograms for structural loads, material quantities, and equipment weights. Key mass references in construction:

• Ready-mix concrete: approximately 2,400 kg per cubic metre
• Structural steel: approximately 7,850 kg per cubic metre
• A standard brick: approximately 2.5 kg
• A 50 kg bag of cement: the most common construction unit of cement in most countries
• A loaded concrete truck: approximately 25–30 tonnes total

Common Conversion Mistakes

Confusing metric tonnes and US short tons: This is an extremely common error in international trade. A metric tonne (1,000 kg) is not the same as a US short ton (907 kg) — a difference of about 10%. In commodities trading, this difference has significant financial implications.

Forgetting that stone is only used in the UK: If you receive a weight in stones from a British source and convert it to kilograms for medical or technical use, remember that 1 stone = 14 lbs = 6.35 kg. This unit is not used in Australia, the US, Europe, or most other countries.

Using weight ounces instead of troy ounces for precious metals: Gold, silver, and platinum prices are always quoted per troy ounce (31.1035 g) not per standard avoirdupois ounce (28.3495 g). Using the wrong ounce when calculating precious metal values gives a result about 10% too low.

Rounding errors in drug calculations: When converting patient weight for drug dosing, use the full precision conversion factor (1 lb = 0.453592 kg) rather than the rounded value (0.45 kg). For a 200 lb patient the difference is 90.7 kg vs 90 kg — small but potentially significant for narrow therapeutic index drugs.

Frequently Asked Questions

Q: What is the easiest way to convert kg to lbs in my head? The most useful mental shortcut is to multiply by 2 and add 10%. For example 70 kg: 70 × 2 = 140, plus 10% = 14, total = 154 lbs. The actual answer is 154.32 lbs — very close. For the reverse (lbs to kg): divide by 2 and subtract 10%. 154 lbs: 154 ÷ 2 = 77, minus 10% = 7.7, total = 69.3 kg. Actual answer: 69.85 kg. Close enough for everyday purposes.

Q: Why is the pound abbreviated as lb? The abbreviation lb comes from the Latin word libra, meaning scales or balance. The full Latin term was libra pondo (pound weight) — libra referring to the balance used to weigh, and pondo meaning weight. Over time the unit took its name from pondo (giving us pound) but kept its abbreviation from libra (giving us lb).

Q: What is the heaviest naturally occurring element by density? Osmium is the densest naturally occurring element at approximately 22,590 kg per cubic metre — more than twice the density of lead (11,340 kg/m³) and about 22 times denser than water. A cube of osmium 10 cm × 10 cm × 10 cm would weigh 22.59 kg. For comparison, the same size cube of aluminium would weigh only 2.7 kg.

Q: How accurate are bathroom scales? Most consumer bathroom scales are accurate to within ±0.1 to ±0.5 kg. For the most accurate reading: weigh yourself at the same time each day (morning, after using the bathroom, before eating), on a hard flat floor (carpet reduces accuracy), and with the scale calibrated to zero before stepping on. Digital scales are generally more accurate than analogue dial scales.

Q: Why do some countries use kg and others use lbs? Most of the world adopted the metric system during the 19th and 20th centuries, with the kilogram as the standard unit of mass. The United States retained the imperial system due to the cost and disruption of converting existing infrastructure, tools, and cultural conventions. The UK officially adopted metric in 1965 but pounds and stones remain in common use for body weight and some food products. Australia, Canada, and New Zealand fully metricated in the 1970s.

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This article is for educational and informational purposes. Medical weight conversions for drug dosing must always be verified by a qualified healthcare professional. Engineering mass calculations must be verified against applicable standards and confirmed by a qualified engineer.