Weight Conversion Calculator Hub

A weight conversion calculator converts a weight from one unit to another, such as kilograms to pounds, ounces to grams, or stone to kilograms. It exists because different countries and different contexts, from cooking to shipping to body weight tracking, still use different weight units in daily life.

This hub covers the concepts, systems, and factors behind weight conversion in general, then links out to a dedicated calculator for each specific unit pair, such as kg to lbs or oz to grams, so a reader can jump straight to the exact tool they need.

Every conversion factor referenced on this page is drawn from fixed international definitions rather than rough estimates, which is explained in full further down. The specific unit pair calculators linked later in this page each apply these same fixed relationships.

What does a weight conversion calculator do?

The calculator takes a starting unit, a target unit, and a value, then returns the converted figure instantly. A user might select kilograms as the starting unit, pounds as the target, enter 70, and receive 154.3 as the result.

Because weight conversion spans a wide range of possible unit pairs, from common ones like kg to lbs to more specialized ones like troy ounces for precious metals, this hub page is built to explain the underlying systems and factors first, then route the reader to the dedicated calculator built for their exact pair. That structure is reflected in how the rest of this page is organized.

Some versions of the tool also handle mixed-unit figures, such as a weight expressed as stone and pounds together rather than a single number, which is common in UK body weight tracking and is covered in its own section below.

Who typically uses a weight conversion calculator?

Home cooks use it mid-recipe, converting ingredient weights between grams and ounces when a recipe and a kitchen scale use different units.

People tracking body weight use it to move between kilograms, pounds, or the stone-and-pounds format common in the UK and Ireland, especially when using fitness apps or medical records that default to a different unit than the one they think in.

Parents use it to convert a baby's weight, translating between the kilogram figures common on medical growth charts and the pounds-and-ounces format used in everyday conversation.

Shoppers and shippers use it when filling out customs forms, postage labels, or freight paperwork that require a specific unit, often different from the one a scale or product listing shows.

Students and generally curious readers use it to look up a specific factual conversion, such as how many pounds are in a stone, without necessarily needing the calculator itself.

What are the main weight measurement systems?

Weight units in everyday use fall into three broad systems. The metric system, built around the kilogram, is the global standard for science, most countries, and international trade. The imperial and US customary system, built around the pound, remains in everyday use in the United States and, for certain units like the stone, in the UK and Ireland. The troy system is a narrower, specialized case, used specifically for weighing precious metals.

Most everyday conversions a reader searches for involve only the first two systems. Troy weight comes up far less often, but is worth understanding on its own since confusing it with the everyday ounce is a common source of error, covered in its own section below. Each system is explained individually in the following three sections.

What is the metric weight system?

The metric system is built around the kilogram as its base unit of mass, historically defined as the weight of one liter of water. The gram, one thousandth of a kilogram, is used for smaller quantities such as cooking ingredients or jewelry, while the metric ton, equal to 1,000 kilograms, is used for large-scale weights like freight or vehicles.

Because the metric system scales entirely in powers of ten, converting between its own units, gram to kilogram or kilogram to tonne, is simply a matter of shifting a decimal point rather than applying an irregular multiplier. This is different from the imperial system covered next, where the unit relationships are fixed but not decimal-based.

What is the imperial and US customary weight system?

The pound is the base unit of this system, and it divides into 16 ounces. The stone, equal to 14 pounds, is used mainly in the UK and Ireland for expressing body weight, while the ton, in either its US short or UK long form, is used for larger weights, both covered in more detail further down this page.

Unlike the metric system, these units do not scale by powers of ten. Sixteen ounces to a pound and fourteen pounds to a stone are both fixed relationships rather than decimal ones, which is why converting within this system, such as pounds to ounces, still requires applying a specific multiplier rather than simply moving a decimal point.

What is the troy weight system?

Troy weight is an older, separate system used specifically for precious metals such as gold and silver. A troy ounce is heavier than the everyday avoirdupois ounce used for cooking or body weight, equal to approximately 31.1035 grams compared to the avoirdupois ounce's 28.3495 grams.

This difference matters because using the wrong ounce type produces a meaningfully wrong result. A reader pricing gold by weight who applies the everyday cooking ounce factor instead of the troy figure will underestimate the true weight by close to 10 percent. Troy weight applies to a narrower set of situations than the metric or imperial systems, mainly precious metals and, in some cases, gemstones, which use the related carat unit instead.

What are the most common weight units and how do they relate to each other?

A small number of unit relationships account for most weight conversion searches. These relationships are the building blocks behind both this page and each of the dedicated unit-pair calculators linked further down. The sections below give the exact figure for each of the most commonly needed pairs.

How many pounds are in a kilogram?

One kilogram equals approximately 2.20462 pounds. This figure is not a rough estimate. It follows directly from the exact NIST definition that one pound equals 453.59237 grams, which means the kilogram-to-pound relationship can be calculated to as many decimal places as needed.

For quick mental math, multiplying by 2.2 instead of the full 2.20462 gives a result accurate to within about 0.2 percent, which is close enough for everyday use like checking body weight, but not precise enough for shipping labels, medical records, or legal documents, where the fuller figure should be used instead. A 70 kg person, for example, weighs approximately 154.3 pounds using the precise factor.

How many grams are in an ounce?

One avoirdupois ounce, the everyday ounce used in cooking and body weight, equals approximately 28.3495 grams. This is distinct from the troy ounce covered earlier on this page, which is heavier and used specifically for precious metals, so the two should not be used interchangeably.

A common cooking reference point is that 8 ounces, or half a pound, works out to about 226.8 grams, useful for quickly checking whether a converted ingredient amount looks reasonable.

How many pounds are in a stone?

One stone equals exactly 14 pounds, and by extension exactly 6.35029318 kilograms. Because UK and Irish body weight is often expressed as a mixed figure, such as 11 stone 4 pounds, rather than a single number, converting this kind of figure to kilograms takes an extra step compared to a single-unit conversion.

Working in the other direction, from kilograms back to stone, follows the same logic in reverse: divide the kilogram figure by 6.35029318 to get a decimal stone value, where the decimal portion represents the leftover pounds.

How many kilograms are in a metric ton?

One metric ton, also called a tonne, equals exactly 1,000 kilograms. This follows the same power-of-ten logic already explained in the metric system section above, so no separate multiplier is needed beyond shifting the decimal point three places.

How do US short tons and UK long tons differ?

A US short ton equals 2,000 pounds, or approximately 907.18 kilograms. A UK long ton equals 2,240 pounds, or approximately 1,016.05 kilograms. The two share the word ton but differ by more than 100 kilograms, which matters most in shipping and freight calculations where the wrong ton definition can meaningfully misstate a weight.

The metric ton, already covered above, sits close to the US short ton in practice but is defined independently through the decimal-based metric system rather than through pounds at all, which is worth keeping separate when comparing all three.

How are weight conversion factors defined and verified?

Weight conversion factors are not casual approximations. They are fixed relationships set by international agreement and maintained by national standards organizations, which is part of why the same conversion factor produces a consistent result no matter which calculator or reference table a reader uses. The two sections below cover who maintains these standards and why some everyday conversions still use rounded figures despite the underlying factor being exact.

Who sets the official standard for weight conversion factors?

The international avoirdupois pound has been defined as exactly 0.45359237 kilograms since a 1959 international agreement. This standard is maintained by national metrology institutes, including the US National Institute of Standards and Technology and the United Kingdom's National Physical Laboratory, operating under the broader framework of the International Bureau of Weights and Measures.

Every other imperial-to-metric weight conversion referenced on this page, including ounces and stones, is derived mathematically from this single fixed pound-to-kilogram relationship rather than being defined independently, which is why all of these figures stay mutually consistent with each other.

Why do some quick conversions use rounded numbers?

Everyday shortcuts, like multiplying kilograms by 2.2 to estimate pounds, use a rounded version of the exact 2.20462 factor because the small difference rarely matters for daily tasks such as checking body weight or estimating how much a package weighs before deciding on shipping options.

For shipping labels, medical records, scientific work, or legal documents, the fully precise, unrounded factor should be used instead of the rounded shortcut, since small rounding errors can compound into a meaningful discrepancy once weights get larger or the context requires exact figures.

What is the difference between mass and weight?

Mass measures the amount of matter contained in an object and stays constant no matter where that object is. Weight is the force exerted on that mass by gravity, which means, in strict physics terms, an object's weight can technically change depending on the gravitational pull acting on it, even though its mass does not.

In everyday, non-scientific contexts, including this page and every calculator it links to, the two terms are used interchangeably, and that is standard, ordinary usage rather than a mistake. The distinction mainly becomes relevant in a scientific or engineering context, where the difference between mass and gravitational force actually changes a calculation.

How does weight conversion fit into everyday tasks like cooking, fitness, and travel?

The general concepts and factors covered above show up constantly in specific, everyday situations. A recipe written in grams needs converting for a cook who only has an ounce-marked scale. A body weight tracked in kilograms at a doctor's office needs converting for someone used to thinking in pounds or stone. A shipping form might ask for a weight in a unit different from the one shown on a home scale.

Rather than explain every one of these situations in full on a single page, this hub connects each specific unit pair to its own dedicated calculator, so a reader can go directly to the exact tool built for their situation. The sections below cover each of those pairs and where to find the full calculator for it.

How do you convert kg to lbs?

This is the most frequently searched weight conversion pair, commonly needed for body weight and fitness tracking, using the exact 2.20462 factor already covered earlier on this page. See the Kg to Lbs Calculator for instant conversion of any value.

How do you convert lbs to kg?

This is the reverse of the previous conversion, commonly needed when a reader has a pounds figure, such as from a US scale or shipping label, and needs the metric equivalent for an international form or comparison. See the Lbs to Kg Calculator for the full tool.

How do you convert kg to stone and pounds?

This conversion is especially relevant for UK and Irish readers tracking body weight, since the result is usually expressed as a mixed stone-and-pounds figure rather than a single decimal number, following the same format explained earlier in the stone section of this page. See the Kg to Stone and Pounds Calculator for the full mixed-unit conversion.

How do you convert stone to kg?

This is the reverse of the previous conversion, useful for a reader who has a stone-and-pounds figure and needs a single kilogram number for a form, app, or international comparison. See the Stone to Kg Calculator for the full tool.

How do you convert oz to grams?

This pair is most often needed in cooking and baking, when a recipe lists an ingredient in ounces but a kitchen scale reads in grams, or vice versa, using the 28.3495 gram figure already covered earlier on this page. See the Oz to Grams Calculator for quick conversion of any amount.

How do you convert grams to oz?

This is the reverse of the previous pair, useful when a recipe or product label lists a weight in grams but the reader thinks in ounces. See the Grams to Oz Calculator for the full tool.

How do you convert pounds to ounces?

This conversion, based on the fixed 16 ounces per pound relationship covered earlier on this page, is commonly needed for shipping weight, baby weight tracking, and any situation calling for a more granular figure than whole pounds. See the Pounds to Ounces Calculator for the full conversion.

How do you convert your baby's weight from kg to lbs and oz?

Many parents need to translate a baby's weight between the kilogram figures used on medical charts and the pounds-and-ounces format commonly used in everyday conversation, especially when hospital records and family expectations use different systems. Precision matters more here given how small the numbers involved usually are. See the Baby Weight Converter for a calculator built specifically for this mixed-unit case.

How do you convert metric tons to kg?

This conversion, based on the 1,000 kilograms per tonne relationship already covered on this page, is typically needed for larger-scale weights such as freight, vehicles, or bulk materials rather than everyday personal weight tasks. See the Metric Tons to Kg Calculator for the full conversion.

How does weight relate to BMI calculation?

Body mass index calculations require weight in a specific unit, typically kilograms or pounds depending on the formula used, so a reader tracking weight in one unit may need to convert it before calculating their BMI. This page does not provide health guidance on its own. See the BMI Calculator for that separate calculation.

How do you convert weight for a recipe measured in cups versus grams?

Cups measure volume rather than weight, so converting between cups and grams depends on the specific ingredient's density, unlike the fixed weight-to-weight conversions covered elsewhere on this page. This makes it a different type of conversion from the unit-to-unit weight pairs above. See the Cups to Grams Calculator for the tool that handles ingredient-specific figures.