Is a ton 1,000 kilograms, 907 kilograms or 1,016 kilograms? All three are right, and this weight and mass converter lists them side by side among 69 units, from the electron mass to the mass of the Sun. Behind the three tons sits one anchor: a pound that is exactly 0.45359237 kilograms.
THREE TONS, ONE KILOGRAM
| Ton | Equal to | In kilograms | Against the metric ton |
|---|---|---|---|
| ton (short) | 2,000 pounds | 907.18474 | −9.2815% |
| ton (metric) | 1,000 kilograms | 1,000 | 0% |
| ton (long) | 2,240 pounds | 1,016.0469088 | +1.6047% |
By direct calculation with 50-digit arithmetic.
Weight and Mass Converter
Complete list of weight and mass units
| Unit | 1 unit in kilograms |
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Shaded rows use the updated values of the panel on older tables. A red mark on the left shows units that share one value.
Definition: the Kilogram, the Pound and 69 Units
The kilogram is the base unit of mass in the International System of Units. Since 2019 it is defined by fixing the Planck constant at 6.62607015 × 10-34 in J·s, with the meter and the second defined through the speed of light and the cesium frequency. That change left the size of the unit exactly as it was. The pound is a unit of mass in the imperial and US customary systems: the international avoirdupois pound, the common pound today, is exactly 0.45359237 kilograms and equals 16 avoirdupois ounces.
Around those two anchors the converter lists the SI-prefixed grams from the exagram to the attogram, the three tons, avoirdupois ounces, quarters, hundredweights and stones, troy and apothecary units, the carat and the assay tons, the slug and other gravitational units, the masses of atoms and particles from the dalton to the Planck mass, the masses of the Earth and the Sun, and ancient Hebrew, Greek and Roman units. Six groups of units share one value, such as ton (metric), megagram and tonne, or kilopound and kip, which makes 62 distinct values behind 69 names.
History and Origin
The name kilogram comes from the French “kilogramme”, built from the Greek word for a thousand and the Late Latin “gramma”, a small weight. It is the only SI base unit that carries an SI prefix, a consequence of building the system on the meter-kilogram-second units rather than on centimeter-gram-second units, which created inconsistencies between the electrostatic and electromagnetic systems. The kilogram was first defined in 1794 as the mass of one liter of water at its freezing point, a definition replaced because measuring a volume of water was imprecise and cumbersome. It then became the mass of a cylinder of platinum-iridium alloy, an imperfect measure: the original prototype now weighs 50 micrograms less than other copies of the standard. The current definition, based on the Planck constant, dates from 2019.
The pound descends from the Roman libra, and many definitions of it were used before the international avoirdupois pound. The avoirdupois system was commonly used in the 13th century and was updated to its current form in 1959. It rested on a physical standard pound that could be divided into 16 ounces, a number with three even divisors (8, 4 and 2), which could be why it prevailed over systems that used 10, 12 or 15 subdivisions.
Current Use, and Three Tons
As an SI base unit, the kilogram is used worldwide in nearly all fields, with exceptions such as the United States, where it serves in science, industry, government and the military but typically not in everyday life. There the pound is widely used, often for body weight. In the United Kingdom, which largely uses SI, pounds remain in certain contexts, such as the labeling of packaged foods, where the metric values must also appear, and body weight is often given in pounds and stones, a stone being 14 pounds.
A kg to lbs conversion multiplies by 2.2046226218, which is 1 ÷ 0.45359237, so 15 kg is 33.0693393277 lbs by direct calculation. A grams to ounces conversion multiplies by 0.0352739619, because an ounce is 28.3495231 grams. The converter lists three tons: the short ton of 2,000 pounds, the metric ton of 1,000 kilograms and the long ton of 2,240 pounds. It also lists a UK stone of 14 pounds and a US stone of 12.5 pounds, so a lbs to stone conversion depends on which stone is meant.
Where Older Tables Are Out of Date
Eight entries rest on values that have since been superseded, and this converter uses the current ones. NIST's 2022 pocket card of the fundamental constants lists the (unified) atomic mass unit at 1.66053906892 × 10-27 kg, the electron mass at 9.1093837139 × 10-31 kg and the proton mass at 1.67262192595 × 10-27 kg. A copy of the NIST listing gives 2.176434 × 10-8 kg for the Planck mass and 1.883531627 × 10-28 kg for the muon, another copy 3.3435837768 × 10-27 kg for the deuteron, and a Wikipedia template updated to the 2022 values 1.67492750056 × 10-27 kg for the neutron. Older tables, such as a constants table hosted by Caltech's astronomy group, still carry the previous values of all of these.
The dalton and the unified atomic mass unit are the same unit, as a university dictionary entry reproducing Wikipedia states, so they share one value here.
| Unit | Older value | This converter | Reason |
|---|---|---|---|
| atomic mass unit | 1.6605402 × 10-27 kg | 1.66053906892 × 10-27 kg | 2022 adjustment |
| dalton | 1.66053 × 10-27 kg | 1.66053906892 × 10-27 kg | same unit as above |
| Planck mass | 2.17671 × 10-8 kg | 2.176434 × 10-8 kg | 2022 adjustment |
| electron mass | 9.1093897 × 10-31 kg | 9.1093837139 × 10-31 kg | 2022 adjustment |
| muon mass | 1.8835327 × 10-28 kg | 1.883531627 × 10-28 kg | 2022 adjustment |
| proton mass | 1.6726231 × 10-27 kg | 1.67262192595 × 10-27 kg | 2022 adjustment |
| neutron mass | 1.6749286 × 10-27 kg | 1.67492750056 × 10-27 kg | 2022 adjustment |
| deuteron mass | 3.343586 × 10-27 kg | 3.3435837768 × 10-27 kg | 2022 adjustment |
Frequently Asked Questions
How many pounds are in a kilogram?
2.2046226218, which is 1 ÷ 0.45359237.
How many kilograms are in a pound?
Exactly 0.45359237 for the international avoirdupois pound.
How many grams are in an ounce?
28.3495231, so an ounce is 0.0283495231 kilograms.
How many pounds are in a stone?
14 for the UK stone and 12.5 for the US stone, which is 6.35029318 kg and 5.669904625 kg.
Are the dalton and the atomic mass unit the same?
Yes. They share one value here, 1.66053906892 × 10-27 kg.
Method and sources. Every factor was checked against its exact definition with 50-digit arithmetic. The eight rows above rest on a NIST pocket card, copies of NIST listings and a Wikipedia template, not on all the primary NIST pages.
This converter is provided for general reference. For trade, medical, pharmaceutical or legal work, use the unit and the standard the document specifies. Written by Staff Editorial, NumeraHub.