Converting Between Pounds, Kilograms & Stones

Weight measurement is one of those everyday tasks that becomes confusing the moment you cross a border or read content from another country. An American sees their weight in pounds, a European thinks in kilograms, and someone from the UK or Ireland might use stones and pounds. Recipes, shipping labels, gym equipment, and medical records all use different systems depending on where they were created.

Understanding the relationships between these units, when each one is used, and how to convert between them accurately saves time and prevents costly mistakes.

The Three Common Weight Units

Pounds (lb)

The pound is the primary unit of weight in the United States and is used informally in several other countries. One pound equals 16 ounces. The abbreviation “lb” comes from the Latin word “libra,” which was a Roman unit of weight.

The pound used today is specifically the avoirdupois pound, standardized internationally as exactly 0.45359237 kilograms. There are also troy pounds (used for precious metals) and apothecary pounds (historical pharmaceutical use), but when someone says “pounds” without qualification, they mean avoirdupois pounds.

Americans use pounds for body weight, food packaging, shipping, cooking, and almost every daily weight measurement. Gym equipment in the US is labeled in pounds, and produce at grocery stores is priced per pound.

Kilograms (kg)

The kilogram is the base unit of mass in the International System of Units (SI) and is used by the vast majority of the world’s population. One kilogram equals 1,000 grams and was originally defined as the mass of one liter of water at 4 degrees Celsius (now defined by the Planck constant for precision).

Nearly every country except the United States, Liberia, and Myanmar uses kilograms as the standard unit for body weight, food labels, shipping, and commerce. Scientific research worldwide uses kilograms regardless of the country of origin.

Medical practice is increasingly standardized on kilograms, even in the US. Medication dosing is calculated in milligrams per kilogram of body weight, and hospitals often record patient weights in kilograms to reduce dosing errors.

Stones (st)

The stone is a unit equal to 14 pounds (approximately 6.35 kg). It is used primarily in the United Kingdom and Ireland for measuring body weight. A person in the UK might say they weigh “11 stone 4” meaning 11 stones and 4 pounds, which is 158 pounds or about 71.7 kilograms.

The stone is rarely used outside the British Isles and isn’t recognized in the SI system. However, it remains deeply embedded in British and Irish culture. Fitness magazines, health websites, and even medical practices in the UK commonly reference weight in stones and pounds.

Historically, the stone varied in weight depending on the commodity being weighed. A stone of wool weighed 14 pounds, but a stone of glass was 5 pounds and a stone of lead was 12 pounds. The 14-pound standard became universal in 1835 and is the only definition used today.

Conversion Formulas

The exact conversion factors are:

Pounds to Kilograms: Divide by 2.20462

• 150 lbs / 2.20462 = 68.04 kg

Kilograms to Pounds: Multiply by 2.20462

• 70 kg x 2.20462 = 154.32 lbs

Pounds to Stones: Divide by 14

• 175 lbs / 14 = 12 stone 7 lbs (12 remainder 7)

Stones to Pounds: Multiply stones by 14, then add remaining pounds

• 10 st 6 lbs = (10 x 14) + 6 = 146 lbs

Kilograms to Stones: Multiply by 0.15747

• 80 kg x 0.15747 = 12.6 st, or 12 stone 8.4 lbs

Stones to Kilograms: Multiply stones by 6.35029, add pounds x 0.45359

• 11 st 3 lbs = (11 x 6.35029) + (3 x 0.45359) = 71.21 kg

Quick Mental Math Shortcuts

Exact formulas are great when you have a calculator, but sometimes you need a fast estimate.

Kg to lbs (quick): Double the kilogram value, then add 10 percent of the doubled number. Example: 70 kg becomes 140, plus 14 = 154 lbs. (Actual: 154.32 lbs. Very close.)

Lbs to kg (quick): Halve the pound value, then subtract 10 percent of the halved number. Example: 180 lbs becomes 90, minus 9 = 81 kg. (Actual: 81.65 kg. Reasonably accurate.)

Stones to lbs (exact): Multiply stones by 14 and add the remaining pounds. This one is simple enough to do precisely in your head.

When Each Unit Is Used

Body Weight

In the US, body weight is discussed in pounds. In the UK and Ireland, stones and pounds dominate casual conversation, though medical settings may use kilograms. In mainland Europe, Asia, Africa, South America, and Australia, kilograms are standard.

If you use an international fitness app or community, you will encounter all three systems. Knowing your weight in each unit helps you participate in discussions and follow programs designed for different audiences.

Cooking and Food

American recipes use pounds and ounces for ingredient weights. European and Australian recipes use grams and kilograms. British recipes might use either or both.

Baking is where conversions matter most. Baking relies on precise ratios, and converting between cups (volume) and grams (weight) introduces errors because different ingredients have different densities. A cup of flour weighs about 125-130 grams, but a cup of sugar weighs about 200 grams. When following recipes from another country, weigh your ingredients rather than trying to convert between volume and weight systems.

Shipping and Commerce

International shipping uses kilograms. Even US-based carriers like FedEx and UPS display weights in both pounds and kilograms for international shipments. Customs forms require metric measurements for packages crossing borders.

Product packaging increasingly shows both systems. A bag of rice in an American grocery store might read “5 lb (2.27 kg)” to serve both domestic and international consumers.

Fitness and Gym Equipment

US gyms label equipment in pounds. Barbells, dumbbells, and weight plates display pounds on one side and kilograms on the other in many modern gyms. Olympic weightlifting uses kilograms worldwide, even in the US. Powerlifting competitions may use either system depending on the federation.

If you follow a training program written in kilograms but your gym uses pounds, you need to convert every working set. A common approach is to round to the nearest available plate. For example, a program calling for 60 kg converts to 132.3 lbs, which you would round to 135 lbs (the nearest standard plate combination).

Medical and Scientific

The global medical community is moving toward kilograms as the universal standard. Drug dosages are calculated per kilogram of body weight. Lab values are reported in metric units. The World Health Organization, international medical journals, and global health databases all use kilograms.

In the US, many hospitals now weigh patients in kilograms and record it as such, even though the patient may think of their weight in pounds. This reduces conversion errors in medication dosing, which is a patient safety issue.

Common Conversion Reference Points

Some frequently looked-up conversions:

• 100 lbs = 45.36 kg = 7 st 2 lbs
• 125 lbs = 56.70 kg = 8 st 13 lbs
• 150 lbs = 68.04 kg = 10 st 10 lbs
• 175 lbs = 79.38 kg = 12 st 7 lbs
• 200 lbs = 90.72 kg = 14 st 4 lbs
• 50 kg = 110.23 lbs = 7 st 12.2 lbs
• 75 kg = 165.35 lbs = 11 st 11.3 lbs
• 100 kg = 220.46 lbs = 15 st 10.5 lbs

Use the Tool

Skip the math and convert instantly with our Weight Converter. Enter a value in any unit and get accurate results in pounds, kilograms, stones, grams, and ounces.

Frequently Asked Questions

Why does the US still use pounds instead of kilograms?

The US Metric Conversion Act of 1975 made the metric system the preferred system of weights and measures, but compliance was voluntary. Without mandatory adoption, industries and consumers kept using the customary system. The cost of switching signage, packaging, regulations, and public education has prevented a full transition. Certain sectors like science, medicine, and the military already use metric, but everyday consumer use remains in pounds and ounces.

Is a kilogram a measure of mass or weight?

Technically, the kilogram measures mass (the amount of matter in an object), while weight measures the force of gravity on that mass. On Earth’s surface, the distinction is negligible for everyday purposes, which is why we use “kilogram” interchangeably for both. On the Moon, a 70 kg person would still have a mass of 70 kg but would weigh only about 11.6 kg-force due to weaker gravity.

How do I convert body weight from stones to a BMI calculation?

BMI formulas require weight in either kilograms or pounds. To convert stones to kilograms for BMI: multiply the stone value by 6.35029, then add any extra pounds multiplied by 0.45359. For example, 12 stone 8 pounds = (12 x 6.35029) + (8 x 0.45359) = 79.83 kg. Then use the standard BMI formula: weight in kg divided by height in meters squared.

Why do British people use stones for body weight but kilograms for everything else?

The UK officially adopted the metric system for trade and commerce in 2000, but personal weight measurement was exempted from mandatory metrication. Stones and pounds remained the cultural norm for body weight because people learned their weight in that system and never had a practical reason to switch. Younger generations in the UK are increasingly comfortable with kilograms, but stones remain dominant in everyday conversation.

Are there any other weight units I should know about?

Ounces (1/16 of a pound) are common for food portions and postal mail in the US. Grams are used worldwide for small measurements like medication and food nutrition labels. Metric tons (1,000 kg) and short tons (2,000 lbs) are used for heavy cargo and industrial measurement. Troy ounces are used exclusively for precious metals like gold and silver, where 1 troy ounce equals 31.1 grams compared to 28.35 grams for a regular ounce.