Weight Converter: kg, lb, oz, Stone and Tonne
What the weight converter does The weight converter changes a value between eleven units of mass: micrograms, milligrams, grams, kilograms, metric tons, ounces, pounds, stone, carats, and the Chinese market units jin (catty) and liang (tael). Enter a number on either side and the other side updates as you type, while the All Units list below shows the same quantity in every unit at once. The conversion factors are exact definitions: the international avoirdupois pound is 0.45359237 kg, an ounce is one sixteenth of a pound, and a stone is fourteen pounds.
The name says weight, but every unit here is a unit of mass, so the converter never consults gravity. For lengths and volumes, use the matching converters (length , volume ).
How to use it 01 Pick the unit you have in the left field and the unit you want in the right field; both dropdowns list the same eleven units. 02 Type a value in the active field; the other field fills in as you type. 03 Expressions work in the active field: 6*7, 1/4 and (1+2)*3 are evaluated before conversion, with a small hint (= 42) as you type; press Enter or = to settle the value. For functions and long chains, use the scientific calculator . 04 The arrow button between the fields swaps the two sides. 05 Click a row in the All Units list to move that unit to the active side; the keypad button opens an embedded calculator. Worked examples Every readout below was produced by this converter.
A five-pound parcel. Set Pound (lb) → Kilogram (kg), type 5. The result reads 2.26796185 kg , and the All Units list adds 80 oz , 2,267.96185 g and 2,267,961.85 mg . The arithmetic is exact: the pound is a defined factor, not a measurement.
Seventy kilograms in pounds. Kilogram (kg) → Pound (lb), type 70: 154.323583529 lb . The exact quotient for 70 ÷ 0.45359237 does not terminate, so the readout stops at 12 significant digits. The same list shows 11.0231131092 st .
Copying a rounded value back. Type 1 kilogram → pound: the readout is 2.2046226219 lb . Now enter that number on the pound side and convert back to kilograms. The kilogram row reads 1 kg , while the microgram row reads 1,000,000,000.02 μg . The re-entered value was a rounded display; the residue only shows at a finer unit.
Where the units come from The metric list is one base unit with prefixes: the kilogram is the SI base unit of mass, the gram is one thousandth of it, and the microgram is a further millionth — which is why 1 kg reads 1,000 g, 1,000,000 mg and 1,000,000,000 μg. Since 2019 the kilogram is defined by the fixed value of the Planck constant; the tonne is accepted for use with the SI and equals 1,000 kg.
The imperial list is avoirdupois, the English wool-trade system that became everyday weights: sixteen ounces to the pound, fourteen pounds to the stone. In 1959 the pound was fixed by international agreement at exactly 0.45359237 kg. The carat is the metric carat of 0.2 g; the list also carries the Chinese market units jin (catty, 0.5 kg) and liang (tael, 50 g).
Reading results and limits
Display rule. Results are displayed rounded to 12 significant digits, then to at most 10 decimal places, with US-style thousands separators: one pound reads 453,592.37 mg . The stored value has more digits than the display, so the last shown digit is a rounded reading of a floating-point number, not the accuracy of the conversion.
Extremes. At the extremes the readout changes shape. Values below 10⁻¹⁰, and values at 10¹⁵ and above, switch to exponential notation with six decimal places; in between, the ten-decimal cap applies:
Prefix jumps. Within those limits larger prefix jumps stay exact: 1 tonne in micrograms reads 1,000,000,000,000 μg .
Input
Readout
Display rule
1 µg in tonnes
1.000000e-12 t below 10⁻¹⁰: exponential
99 µg in tonnes
9.900000e-11 t just under the lower threshold
100 µg in tonnes
0.0000000001 t at the threshold: decimal, capped at 10 places
1,000 tonnes in micrograms
1.000000e+15 μg at 10¹⁵ and above: exponential
Common mistakes
The tool is called a weight converter, but it converts mass. Mass is how much matter an object has; weight is the force gravity exerts on it, measured in newtons. The kilogram, pound, ounce, stone and tonne are all mass units, so gravity never enters the sum: a 70 kg value reads 154.323583529 lb on Earth, on the Moon or in orbit.The oz here is the avoirdupois ounce, 28.349523125 g. A fluid ounce measures volume, so liquid ingredients belong to the volume converter .
The ct is the metric carat, 0.2 g, used for gemstones; gold purity in karats is not a mass and cannot be converted here.
Only the metric tonne is listed, and it is 1,000 kg. A bare "ton" may mean the US short ton or UK long ton instead, which this list does not include.
Don't treat the last displayed digit as exact; round at the end, and don't add digits your scale never measured.
Where it is used
Parcels and shipping. A five-pound parcel is 2.26796185 kg for a customs form, and the kilogram scale reads the reverse.Body weight and diet. Kilograms to pounds and stone for a scale that reports only one system: 70 kg is 154.323583529 lb and 11.0231131092 st.Kitchen and market measures. Grams to ounces for a recipe, carats for gemstones, and the Chinese market units jin (0.5 kg) and liang (50 g). Privacy All input and calculation run inside your browser and are never uploaded. This page is static text; it neither contains nor records user input.
Sources
BIPM, The International System of Units (SI Brochure) , 9th edition — the SI base unit of mass, SI prefixes and the tonne's standing with the SI. bipm.org （访问日期：2026-09-30）
NIST Special Publication 811, Appendix B.9 — mass conversion factors, including the metric carat and the metric, short and long tons. nist.gov （访问日期：2026-09-30）
Weights and Measures Act 1985 , Schedule 1 — the pound as 0.45359237 kg, the ounce as 1/16 pound, the stone as 14 pounds, the metric ton as 1,000 kg and the carat as 0.2 g. legislation.gov.uk （访问日期：2026-09-30）Wikipedia, Avoirdupois — the sixteen-ounce pound, the fourteen-pound stone and the 1959 international agreement. en.wikipedia.org （访问日期：2026-09-30）
Sources & review
Reviewed by CalcX Editorial Team
Updated 2026-09-30