Weight Converter
Example 1
An airline allows checked luggage up to 23 kg per bag. A traveller from the United States weighs their suitcase at home and the scale reads 45 lb. They need to know if the suitcase is under the weight limit.
Solution
The conversion from pounds to kilograms uses the factor 1 lb = 0.453592 kg. For 45 lb: 45 lb × 0.453592 kg/lb = 20.412 kg.
The suitcase at 20.4 kg is under the 23 kg limit by 2.6 kg. For mental estimation, dividing the weight in pounds by 2.2 gives a close approximation: 45 ÷ 2.2 ≈ 20.45 kg. This quick check can be done at the airport without a calculator. The exact conversion factor 0.453592 comes from the international pound agreement of 1959, when English-speaking countries standardised the pound as exactly 0.45359237 kg.
Answer
20.4 kg. A 45 lb suitcase converts to 20.4 kg, which is under the 23 kg airline limit by 2.6 kg, leaving room for additional souvenirs.
Source: International Air Transport Association: Baggage Guidelines
Example 2
A baker in the United Kingdom follows an American recipe that calls for 4 oz (ounces) of butter. The baker’s digital scale measures in grams and they need the correct metric equivalent.
Solution
The avoirdupois ounce is the standard for cooking: 1 oz = 28.3495 g. For 4 oz: 4 oz × 28.3495 g/oz = 113.398 g.
Rounding to the nearest gram gives 113 g, which is the standard conversion used in UK baking. However, many British recipes use the metric conversion 1 oz ≈ 25 g for rough estimates, which would give only 100 g for 4 oz. This difference of 13 g can affect the texture of baked goods, especially in recipes where butter is a primary ingredient. Professional bakers use the exact conversion factor for consistent results. For butter, a stick of butter in the US is 4 oz or 113 g, which matches this conversion exactly.
Answer
113 g. Four ounces of butter converts to approximately 113 g. Using the rounded conversion of 25 g per ounce would short the recipe by 13 g, potentially affecting baking results.
Source: USDA National Nutrient Database for Standard Reference
Example 3
A person weighing 165 lb visits a doctor in a country that uses the metric system. The medical record requires weight in kilograms, and Body Mass Index (BMI) calculations also require metric weight.
Solution
Using the conversion factor 1 lb = 0.453592 kg: 165 lb × 0.453592 kg/lb = 74.843 kg.
Medical records typically record weight to one decimal place, giving 74.8 kg. The BMI calculation requires weight in kilograms and height in metres. For a person 1.78 m tall, BMI = 74.8 ÷ (1.78)² = 23.6 kg/m², which falls in the normal weight range (18.5 to 24.9). The approximate conversion dividing pounds by 2.2 gives 165 ÷ 2.2 = 75 kg, which is within 0.2 per cent of the exact value and is close enough for most medical screening purposes.
Answer
74.8 kg. A body weight of 165 lb converts to 74.8 kg. This metric value is used for BMI calculation, medication dosing, and international health records.
Source: WHO: Physical Status: The Use and Interpretation of Anthropometry
Example 4
A patient weighs 175 lbs. The physician needs weight in kilograms and stone for the medical record.
Solution
1 lb = 0.0714286 stone. 175 × 0.0714286 = 12.5 stone (12 st 7 lbs).
Answer
175 lbs = 79.4 kg = 12 st 7 lbs.
Published:
Updated:
References
- [1]Bureau International des Poids et Mesures (BIPM), The International System of Units (SI) - 9th Edition, 2019. https://www.bipm.org/en/publications/si-brochure
- [2]National Institute of Standards and Technology (NIST), NIST Guide for the Use of the International System of Units (SI), 2008. https://physics.nist.gov/cuu/pdf/sp811.pdf
- [3]International Organization for Standardization (ISO), ISO 80000-4: Quantities and Units - Part 4: Mechanics, 2019.
Glossary
- Mass – A measure of the amount of matter in an object, independent of gravity. Mass is an intrinsic property measured in kilograms (kg) and remains constant regardless of location in the universe.
- Weight – The force exerted on a mass by gravity, measured in newtons (N). Weight varies with gravitational field strength and is often used interchangeably with mass in everyday contexts but is technically distinct.
- Kilogram (kg) – The SI base unit of mass, defined by the Planck constant. The kilogram is the only base unit with a prefix and is the standard for all mass measurements worldwide.
- Pound (lb) – A unit of mass in the imperial and US customary systems, defined as exactly 0.45359237 kg by international agreement since 1959. The pound is used for body weight, food, and commerce in the US and UK.
- Ounce (oz) – A unit of mass equal to 1/16 of a pound or exactly 28.3495 grams. The avoirdupois ounce is used in cooking, postal services, and precious metal trading.
- Gram (g) – A metric unit of mass equal to 1/1,000 of a kilogram. Grams are used for small masses in cooking, laboratory measurements, and nutrition labelling worldwide.
- Tonne (t) – A metric unit of mass equal to 1,000 kg, also called a metric ton. The tonne is used for industrial quantities, vehicle weights, and bulk commodity trading.
- Stone (st) – A British imperial unit of mass equal to 14 pounds or approximately 6.35 kg. Body weight in the UK and Ireland is commonly expressed in stones and pounds.
- Gravity – The acceleration due to gravitational attraction, approximately 9.81 m/s² on Earth’s surface. Gravity varies slightly with latitude and altitude, affecting weight but not mass.
- International pound – The standardised pound defined in 1959 by the US, UK, Canada, Australia, New Zealand, and South Africa as exactly 0.45359237 kg, replacing earlier regional variations.
How to Use?
- 1
Enter the weight value
Type the numeric value you want to convert into the Value field.
- 2
Select the source unit
Choose the unit of your input value from the unit dropdown: mg, g, kg, t, oz, lb, st, US ton, or UK ton.
- 3
Choose the display unit
Use the Display Result In dropdown to select which unit appears highlighted as the primary result.
- 4
Review the result
The result panel shows your value in the chosen display unit, with all other supported units listed as alternatives below it.
- 5
Cross-check key conversions
Use the reference table to verify common factors: 1 kg = 2.205 lb, 1 lb = 454 g, 1 st = 6.35 kg.
- 6
Explore related converters
Use the volume, length, or pressure converters linked on this page for additional unit conversion needs.
Frequently Asked Questions
Yes, this converter supports all nine units: milligrams (mg), grams (g), kilograms (kg), tonnes (t), ounces (oz), pounds (lb), stones (st), US short tons, and UK long tons. Select your source unit from the dropdown and the tool displays all equivalents instantly.
Conversions are based on internationally accepted values defined by the International System of Units (SI). The pound is defined as exactly 0.45359237 kg by the 1959 International Yard and Pound Agreement. Results are displayed with up to four decimal places for the primary result and appropriate precision for all alternative units.
One pound equals exactly 453.59237 grams by international agreement. For quick mental estimation, 1 lb ≈ 454 g is a common approximation, but for precise work use the full factor. The converter applies the exact factor internally and rounds only at display time.
A stone is a unit of mass equal to 14 pounds (6.35029 kg). It is primarily used in the United Kingdom and Ireland for measuring body weight. A person weighing 12 stone is approximately 76.2 kg. The stone is rarely used in the United States or continental Europe for any measurement.
One avoirdupois ounce equals 28.349523125 grams. To convert ounces to grams, multiply by 28.35. For cooking, 1 oz ≈ 28 g is a common approximation. Note that troy ounces (31.1035 g) are used for precious metals and are different from the avoirdupois ounces used in this converter.
A metric tonne equals 1,000 kg (2,204.62 lb). A US short ton equals 2,000 lb (907.185 kg). A UK long ton equals 2,240 lb (1,016.05 kg). The short ton is about 9.3% lighter than the long ton, and the metric tonne falls between them. This converter includes all three to avoid ambiguity in industrial and commercial applications.
One stone equals 6.35029 kg. To convert stones to kilograms, multiply by 6.35. For example, 12 stone × 6.35 = 76.2 kg. To convert stones and pounds, first convert the pounds to a decimal fraction of a stone (divide by 14), add to the stones, then multiply by 6.35. This converter handles the calculation instantly.
Most countries mandate metric units (grams) for food labelling by law. In the United States, the FDA requires Nutrition Facts labels to show serving sizes in both grams and ounces, but grams are the primary unit. The European Union requires grams and millilitres. This dual-labelling exists because consumers in each country are familiar with their local measurement system for food quantities.
One gram equals exactly 1,000 milligrams. This is a core relationship of the metric mass system. To convert grams to milligrams, multiply by 1,000. To convert milligrams to grams, divide by 1,000. The same relationship applies between kilograms and grams: 1 kg = 1,000 g.
One pound contains exactly 16 avoirdupois ounces. Each ounce equals 28.3495 grams, so 1 lb = 16 × 28.3495 g = 453.592 g. This 16-ounce-per-pound relationship is the same in both the US customary and UK Imperial systems for everyday weight measurements.
Mass measures the amount of matter in an object and is constant regardless of location. Weight measures the gravitational force on that mass and varies with gravity. An object with a mass of 10 kg weighs about 98 N on Earth and about 16 N on the Moon, but its mass is 10 kg in both places. This converter works with mass values, not weight force. For everyday purposes on Earth, the distinction is rarely significant, but it matters in aerospace and high-precision science.
To convert stones and pounds to kilograms: multiply the stones by 6.35029, convert the extra pounds to kilograms (divide by 2.20462), and add the two results. For example, 11 stone 8 lb: (11 × 6.35029) + (8 ÷ 2.20462) = 69.85 + 3.63 = 73.48 kg. To convert kilograms to stones and pounds: multiply by 0.15747 to get the decimal stone value, take the whole number as stones, multiply the decimal part by 14 to get the remaining pounds.
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