What is the difference between mass and weight?

Mass is the amount of matter (kg or lb-mass). Weight is the force of gravity on that mass (newtons or lb-force). On Earth 1 kg weighs 9.8 N, on the Moon 1 kg weighs 1.6 N.

How do I convert between kilograms and pounds?

kg to lb: multiply by 2.20462. 75 kg = 165.35 lb. lb to kg: divide by 2.20462.

How does density relate mass and volume?

Density = mass / volume. Given any two, calculate the third. Includes built-in densities for common materials like water, steel, air.

How many ounces in a pound and pounds in a stone?

16 oz in 1 lb. 14 lb in 1 stone. So 1 stone = 14 lb = 224 oz.

What is the difference between a metric ton and a US ton?

Metric ton = 1000 kg (2204.6 lb). US short ton = 2000 lb (907.2 kg). UK long ton = 2240 lb (1016 kg).

Mass Calculator

From Unit

Value

Introduction

Mass is a fundamental property of matter that measures the amount of substance in an object. Unlike weight, which varies with gravity, mass is an intrinsic property that remains constant regardless of location. In the International System of Units (SI), the base unit of mass is the kilogram (kg), defined as the mass of the International Prototype Kilogram, a platinum-iridium alloy cylinder stored at the BIPM in Sèvres, France.

Different regions and fields use different mass units. The metric system (kilograms, grams, milligrams, tonnes) is standard in most of the world and in scientific work. The imperial and US customary systems use pounds, ounces, stones, and short tons, which remain common in the United States, the United Kingdom, and several other countries. Navigating between these systems can be tedious and error-prone when done manually.

This Mass Calculator converts between all common mass units instantly. Enter a value in any unit, and the calculator displays the equivalent in every other supported unit simultaneously. No need to memorize conversion factors or do arithmetic by hand. Whether you are a chef adjusting recipes, a student completing homework, a scientist conducting experiments, or a business dealing with international trade, this tool provides instant, accurate conversions across eleven different mass units.

How to Use

Using the Mass Calculator is intuitive and requires no special training. Follow these simple steps to perform conversions:

Select the input unit from the dropdown menu. Choose from milligram (mg), gram (g), kilogram (kg), tonne (t), ounce (oz), pound (lb), stone (st), hundredweight (cwt), US short ton, UK long ton, or carat (ct). The dropdown contains all supported units with their abbreviations clearly displayed.
Enter a numeric value in the input field. You can enter whole numbers or decimal values. The calculator accepts both positive and negative values, though negative mass values will generate an error since they have no physical meaning.
View all equivalent values in the results table, which updates in real time as you type or change the unit. Every supported unit shows its converted value immediately, allowing you to see how your input relates to all other units simultaneously.
Check for errors if you see a red error message. Common issues include entering negative numbers (which are physically impossible) or values exceeding one billion (the maximum input limit to prevent display issues).

The calculator supports values with decimal precision. Results are displayed with up to six significant digits of accuracy, which is sufficient for virtually all practical applications.

Real-World Examples

Converting Recipe Ingredients

Imagine you are following a British recipe that calls for 500 grams of flour, but your measuring cup only shows ounces. Simply enter "500" in the input field, select "Gram (g)" as the unit, and instantly see that this equals approximately 17.64 ounces (oz). Conversely, if you have 8 ounces of butter and need to know how many grams that is, select "Ounce (oz)", enter "8", and see the result is 226.80 grams.

International Shipping Calculations

A shipping company needs to determine the weight of a container in different units for documentation purposes. If the container weighs 15 tonnes (metric tons), the calculator shows this equals 16.53 US short tons, 14.76 UK long tons, or 15,000 kilograms. This helps logistics professionals complete paperwork for different countries with different preferred units.

Laboratory Work

A chemistry student needs to measure 250 milligrams of a chemical compound but only has a scale that displays in grams. Enter "250" with "Milligram (mg)" selected, and the calculator shows this equals 0.25 grams, 0.00025 kilograms, or 1.25 carats.

Body Weight in Different Countries

A person weighing 180 pounds wants to know their weight in stones (commonly used in the UK). Enter "180" with "Pound (lb)" selected, and the result shows this equals approximately 12.86 stones. This is useful for British immigrants who grew up using stones but now live in countries using kilograms.

History of Mass Units

Metric System Origins

The metric system was introduced in France in 1795 during the French Revolution. Before this, measurement standards varied wildly between regions, making trade and scientific communication difficult. The French Academy of Sciences defined the kilogram as the mass of one liter of water at 4°C, though this definition was later refined to use a physical artifact. The metric system spread throughout Europe and the world through Napoleonic conquests and international treaties.

Imperial and US Customary Systems

The imperial system originated in the British Empire and traces its roots to Roman and Anglo-Saxon measurements. The pound was historically defined as the weight of silver coins, though this evolved over centuries. The British standardized the system in 1824 with the Weights and Measures Act. The United States adopted its own version of the imperial system in 1790, retaining many British units but diverging in some definitions. The US customary system differs from the British imperial system in several ways, most notably in volume measurements and the hundredweight.

The Kilogram-to-Pound Relationship

The precise conversion between kilograms and pounds (1 kg = 2.2046226218 lb) was established through international agreement. This conversion factor is used by all nations and is critical for international trade, scientific research, and everyday conversions. The value is precise because it is defined by international treaty rather than being an approximation.

Formulas and Calculations

Metric Conversions

The metric system is decimal-based, making conversions within it straightforward:

1 \, \text{kg} = 1000 \, \text{g}

1 \, \text{g} = 1000 \, \text{mg}

1 \, \text{tonne (metric ton)} = 1000 \, \text{kg} = 1\,000\,000 \, \text{g}

1 \, \text{kg} = 0.001 \, \text{tonnes}

Imperial and US Customary Conversions

The imperial and US customary systems use non-decimal relationships:

1 \, \text{lb} = 16 \, \text{oz}

1 \, \text{stone} = 14 \, \text{lb}

1 \, \text{US short ton} = 2000 \, \text{lb}

1 \, \text{UK long ton} = 2240 \, \text{lb}

Metric to Imperial Conversion Factors

The key bridge between the two systems:

1 \, \text{kg} = 2.2046226218 \, \text{lb}

1 \, \text{lb} = 0.45359237 \, \text{kg}

1 \, \text{g} = 0.0352739619 \, \text{oz}

1 \, \text{oz} = 28.349523125 \, \text{g}

1 \, \text{stone} = 6.35029318 \, \text{kg}

Converting Between Any Two Units

To convert from a source unit to a target unit:

m_{\text{target}} = m_{\text{source}} \times \frac{f_{\text{target}}}{f_{\text{source}}}

where f~~unit~~ is the conversion factor from that unit to kilograms. The calculator internally converts all inputs to kilograms as an intermediate step, then converts from kilograms to every output unit.

Reference Table

Unit	Abbreviation	Equivalent in kg
Milligram	mg	0.000001 kg
Gram	g	0.001 kg
Kilogram	kg	1 kg
Tonne (metric ton)	t	1000 kg
Ounce	oz	0.028349523125 kg
Pound	lb	0.45359237 kg
Stone	st	6.35029318 kg
Hundredweight (US)	cwt	45.359237 kg
US Short Ton	tn	907.18474 kg
UK Long Ton	lt	1016.0469088 kg
Carat	ct	0.0002 kg

Common Applications by Field

Cooking and Food Industry

Different countries use different units for food labeling and recipes. The European Union requires metric units on food labels, while the United States uses customary units. Professional chefs working with international recipes frequently convert between grams, ounces, and pounds.

Healthcare and Medicine

Medical dosages are typically measured in milligrams or micrograms for precision. Healthcare professionals working internationally often need to convert patient weights between kilograms and pounds for medication dosing.

Engineering and Construction

Structural engineering uses different units depending on the country. Steel beams might be specified in kilograms per meter in one country and pounds per foot in another.

Precious Metals and Jewelry

The jewelry industry commonly uses carats for gemstones and troy ounces for precious metals. Note that this calculator uses the metric carat and avoirdupois ounce, not the troy ounce used for precious metals.

Agriculture and Commodities

Grain, produce, and other commodities are traded using different units internationally. Understanding these conversions is essential for farmers and commodity traders.

Limitations

This calculator uses international avoirdupois definitions for imperial and US customary units. It does not support troy weight, apothecaries' weight, or precious-metal units (such as troy ounces or troy pounds), which use different conversion factors.

Precision is limited to six significant digits. For applications requiring more than six digits of precision (such as high-precision scientific metrology or legal trade calibration), refer to the original NIST and BIPM published values.

Results may show minor rounding in the final displayed digit due to floating-point arithmetic. The calculator does not support negative mass values, as these have no physical meaning.

Frequently Asked Questions

What is the difference between mass and weight?: Mass is the amount of matter (kg or lb-mass). Weight is the force of gravity on that mass (newtons or lb-force). On Earth 1 kg weighs 9.8 N, on the Moon 1 kg weighs 1.6 N.
How do I convert between kilograms and pounds?: kg to lb: multiply by 2.20462. 75 kg = 165.35 lb. lb to kg: divide by 2.20462.
How does density relate mass and volume?: Density = mass / volume. Given any two, calculate the third. Includes built-in densities for common materials like water, steel, air.
How many ounces in a pound and pounds in a stone?: 16 oz in 1 lb. 14 lb in 1 stone. So 1 stone = 14 lb = 224 oz.
What is the difference between a metric ton and a US ton?: Metric ton = 1000 kg (2204.6 lb). US short ton = 2000 lb (907.2 kg). UK long ton = 2240 lb (1016 kg).

References

Bureau International des Poids et Mesures (BIPM). The International System of Units (SI), 9th edition, 2019. https://www.bipm.org/en/publications/si-brochure
National Institute of Standards and Technology (NIST). Special Publication 811: Guide for the Use of the International System of Units (SI), 2008. https://www.nist.gov/pml/special-publication-811
International Bureau of Weights and Measures. The International System of Units (SI) Brochure. Updated 2019.
National Physical Laboratory (UK). Guide to the System of Units. Updated 2023.

Last updated: May 28, 2026