Weight & Mass Converter
Kilograms, pounds, stones, ounces, tonnes and the two tons that are not tonnes. Enter one figure and read it in every unit at once — on the exact defined factors, not on decimals someone rounded.
Convert a mass
The figure you have, in the unit chosen below.
The unit the figure is already in.
The unit you want the answer in. Every other unit is listed underneath the result anyway.
Everything routes through the kilogram: 70 kg is 70 kg, and one lb is exactly 0.45359237 kg.
- Conversion factor
- 1 kg = 2.204622622 lb
- Reverse factor
- 1 lb = 0.45359237 kg
- In kilograms
- 70 kg
- Definition
- One avoirdupois pound is exactly 0.45359237 kg, fixed by the 1959 international yard and pound agreement.
| Unit | Symbol | Value |
|---|---|---|
| Milligrams | mg | 70,000,000 |
| Grains | gr | 1,080,265.085 |
| Carats | ct | 350,000 |
| Grams | g | 70,000 |
| Ounces | oz | 2,469.177336 |
| Pounds | lb | 154.3235835 |
| Kilograms | kg | 70 |
| Stones | st | 11.02311311 |
| US short tons | short tn | 0.07716179176 |
| Tonnes | t | 0.07 |
| Imperial long tons | long tn | 0.06889445693 |
Every conversion goes through the kilogram
Eleven units could be connected by 121 direct factors, and a table that size cannot be kept consistent. Instead each unit is stored as one number — how many kilograms it is — and every conversion is two steps.
kilograms = value × f(from) • result = kilograms ÷ f(to)- f(u)
- Kilograms in one unit u — 0.45359237 for the pound
- kilograms
- The mass in the SI base unit
- result
- The mass in the unit you asked for
What makes this exact rather than approximate is where the factors come from. These are definitions, not measurements:
- 1 pound = 0.45359237 kg exactly. Fixed by the international yard and pound agreement of 1 July 1959, signed by the national standards laboratories of the United States, United Kingdom, Canada, Australia, New Zealand and South Africa. Before it, an American pound and a British pound were very slightly different masses.
- The ounce, grain, stone and both tons all follow from it by whole numbers: the ounce is a sixteenth of a pound, the grain a seven-thousandth, the stone fourteen pounds, the US short ton 2,000 pounds and the imperial long ton 2,240.
- 1 metric carat = 200 mg exactly, set by the General Conference on Weights and Measures in 1907 and adopted in the United States in 1913. It replaced a tangle of local carats that differed from city to city.
- The kilogram itself is defined by the Planck constant — fixed at 6.62607015 × 10⁻³⁴ joule seconds on 20 May 2019. Until that day the kilogram was a platinum-iridium cylinder kept outside Paris since 1889, and it had drifted about 50 micrograms against its own official copies. Every other unit on this page is ultimately a multiple of that constant.
Results are rounded to twelve significant figures rather than to a fixed number of decimal places. A tool that spans milligrams to long tons has no single sensible decimal place — two decimals would turn a milligram into zero. Significant figures are also what makes one pound come back as exactly 7,000 grains: 0.45359237 ÷ 0.00006479891 in binary floating point is 6999.999999999999, and rounding to twelve figures restores the number the definition promises.
This converts mass. Weight is a force.
Almost every converter on the internet is titled “weight” and quietly converts mass. So does this one — the word people search for is weight — but it is worth knowing what the numbers actually are.
Mass is how much matter there is. It is what resists being accelerated, it is the same everywhere in the universe, and its SI unit is the kilogram. Weight is the force gravity exerts on that mass, it changes with where you are standing, and its SI unit is the newton. A 70 kg person weighs about 687 N on Earth and about 114 N on the Moon, while having 70 kg of mass in both places.
A bathroom scale measures force — it reads how hard you press on a spring or a strain gauge — and then divides by an assumed gravity to print a mass. That assumed value is standard gravity, 9.80665 m/s² exactly, agreed by the General Conference on Weights and Measures in 1901. Real gravity varies by roughly 0.5% between the equator and the poles, which is why laboratory balances are recalibrated when they move city.
The pound is genuinely used for both. The pound-mass on a food label is the 0.45359237 kg this page converts; the pound-force in an engineering drawing is the force standard gravity exerts on it, about 4.448 N. They are interchangeable in everyday speech only because standard gravity is a fixed number. This tool converts mass and never asks where you are — which is precisely why its answers hold unchanged in orbit.
70 kilograms in pounds and stones
Step one: 70 × 1 = 70 kilograms, since the kilogram is the base. Step two: 70 ÷ 0.45359237 = 154.3235835 pounds. Read the same 70 kg in stones and it is 11.02311311 st — and because a stone is exactly 14 pounds, that is 11 stone (154 lb) with 0.32 lb, or about 5.2 ounces, left over.
The expensive example is the ton. Take a 40-ton shipment and price it three ways. Forty US short tons is 40 × 907.18474 = 36,287.39 kg. Forty tonnes is 40,000 kg. Forty imperial long tons is 40 × 1,016.0469088 = 40,641.88 kg. Between the smallest and the largest sits 4,354 kg — over four tonnes of cargo that exists or does not depending on which country wrote the contract. Freight rates, crane ratings and axle limits have all been quoted in the wrong ton at some point, and the number is large enough that nobody notices it as a rounding error.
A smaller one that catches cooks: 8 ounces is 226.796185 g, not 250. A US “half-pound” of butter and a European 250 g block differ by about 10%, which matters in pastry and nowhere else.
What this converter assumes
- Every unit here is a mass. Nothing on this page converts to newtons, kilogram-force or pound-force, because those need a value of gravity attached and that is a different question.
- The ounce and the pound are the avoirdupoisones. The troy ounce used for precious metals is 31.1034768 g, about 9.7% heavier, and is deliberately not offered — two things called “ounce” in one menu, with no metal attached to say which is meant, causes more errors than it prevents.
- A mass is a magnitude, so negative values are rejected. If you are converting the difference between two weighings, convert its size and keep the sign yourself.
- Results carry twelve significant figures internally and are displayed to ten. Neither is a claim about your measurement — a bathroom scale reading to the nearest 100 g is still only accurate to the nearest 100 g after conversion.
- No unit here is a volume. A US fluid ounce and an avoirdupois ounce share a name and measure different things; a pint of water weighing a pound is a mnemonic, not a conversion.
Weight and mass conversion FAQ
How many pounds is 70 kg?
154.3235835 pounds. A pound is exactly 0.45359237 kg, so 70 ÷ 0.45359237 = 154.32 lb. In the units a UK bathroom scale uses that is 11 stone and about a third of a pound — 11 st 5 oz.
Is a kilogram weight or mass?
Mass. Mass is how much matter something contains; weight is the force gravity exerts on that mass, and force is measured in newtons. Your bathroom scale actually measures force and reports mass, having been calibrated for standard gravity — 9.80665 m/s² exactly, fixed by the General Conference on Weights and Measures in 1901. This converter never asks where you are, because converting mass does not need gravity: 70 kg is 70 kg on the Moon too, even though you would weigh about a sixth as much there.
How much is a stone in kilograms?
One stone is exactly 14 pounds, or 6.35029318 kg. It was abolished as a legal unit for trade in the United Kingdom by the Weights and Measures Act 1985, and survives in the UK and Ireland almost exclusively for body weight. Nobody buys potatoes by the stone and no other country uses it at all, which is why an American reading '11 stone' usually has to look it up.
Is a ton the same as a tonne?
No, and there are three of them. A US short ton is 2,000 lb (907.18474 kg). A tonne, or metric ton, is 1,000 kg. An imperial long ton is 2,240 lb (1,016.0469088 kg). The long ton is 12% heavier than the short ton and 1.6% heavier than the tonne. On a 40-ton shipment that spread is 4,354 kg — more than four tonnes of cargo that either exists or does not, depending on whose ton the paperwork meant.
Is a troy ounce the same as a normal ounce?
No. A troy ounce, used for gold, silver and platinum, is 31.1034768 g. The avoirdupois ounce this converter uses — the one in recipes and on shipping labels — is 28.349523125 g. The troy ounce is about 9.7% heavier. But a troy pound is only 12 troy ounces, so it comes to 373.24 g, which makes it 18% lighter than the 453.59 g avoirdupois pound. That is the answer to the old riddle: a pound of feathers outweighs a pound of gold, while an ounce of gold outweighs an ounce of feathers.
What is a grain, and why do bullets use it?
A grain is exactly one seven-thousandth of a pound: 64.79891 mg. It is the one unit shared identically by the avoirdupois, troy and apothecaries' systems, which is why it outlived them all. Bullets, arrows and gunpowder charges are still specified in grains, and so were medicines — the standard 5-grain aspirin tablet is 324.5 mg, which is why the modern label reads 325 mg.
Is a carat a weight?
The metric carat is, and it has been exactly 200 mg since the General Conference on Weights and Measures set it in 1907. A 1.5-carat diamond has a mass of 300 mg. Karat, spelled with a k, is something else entirely: it is gold purity in twenty-fourths, so 18 karat is 18/24 gold by mass and no mass at all.
Sources and review notes
- NIST Special Publication 811 — Guide for the Use of the International System of Units (SI), including the exact conversion factors used here
- NIST — the 2019 redefinition of the kilogram in terms of the Planck constant
- BIPM — The International System of Units (SI) Brochure, for the kilogram and for standard gravity
The factors on this page are defined values rather than measured ones, so they do not go stale: the pound has been exactly 0.45359237 kg since 1959 and the metric carat exactly 200 mg since 1907. What changed in 2019 was the definition of the kilogram itself, and it was deliberately chosen to leave every number on this page unaltered.