Weight to Kilograms Converter
Convert weight to kilograms from pounds, ounces, stone, grams, and more. Complete multi-unit weight converter with adjustable precision.
Weight to Kilograms Converter
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Formula: kg = lb x 0.45359237 | kg = oz x 0.028349523 | kg = st x 6.35029318 | kg = g / 1000
Worked example — 175 lb = 79.3787 kg = 12 st 7 lb
Formula
kg = lb x 0.45359237 | kg = oz x 0.028349523 | kg = st x 6.35029318 | kg = g / 1000
All conversions go through grams as the base unit. Each input unit has an exact conversion factor to grams. Kilograms are then derived by dividing grams by 1000. The pound to kilogram factor (0.45359237) is an exact definition established by international agreement.
Worked Examples
Example 1: Body Weight Conversion
Problem:Convert 175 pounds to kilograms and stone.
Solution:Kilograms: 175 x 0.45359237 = 79.3787 kg Stone: 175 / 14 = 12 stone 7 pounds Ounces: 175 x 16 = 2,800 oz Grams: 175 x 453.59237 = 79,378.66 g
Result:175 lb = 79.3787 kg = 12 st 7 lb
Example 2: Shipping Package Weight
Problem:Convert 5.5 kilograms to pounds and ounces for a shipping label.
Solution:Pounds: 5.5 x 2.20462 = 12.1254 lb Whole pounds: 12 lb Remaining ounces: 0.1254 x 16 = 2.0064 oz Total ounces: 5.5 x 35.274 = 194.007 oz
Result:5.5 kg = 12 lb 2 oz = 194.01 oz
Frequently Asked Questions
How do I convert pounds to kilograms?
Multiply the weight in pounds by 0.45359237 to get kilograms. This conversion factor is exact by definition: one pound avoirdupois equals exactly 0.45359237 kilograms. For a quick mental estimate, divide pounds by 2.2. So 150 pounds is approximately 150 / 2.2 = 68.18 kg (exact: 68.0389 kg). The inverse conversion multiplies kilograms by 2.20462262 to get pounds.
What is the difference between avoirdupois and troy weight systems?
The avoirdupois system is used for everyday weighing: 1 pound = 16 ounces = 453.59 grams. The troy system is used for precious metals: 1 troy pound = 12 troy ounces, where 1 troy ounce = 31.1035 grams. A troy ounce is heavier than an avoirdupois ounce, but a troy pound is lighter than an avoirdupois pound. When someone says an ounce of gold, they mean a troy ounce (31.1 g), not an avoirdupois ounce (28.35 g). This converter uses the avoirdupois system unless otherwise noted.
How accurate are kitchen and bathroom scales?
Consumer kitchen scales are typically accurate to 1-2 grams, while bathroom scales are accurate to about 0.1-0.5 kg (0.2-1 lb). Digital scales are generally more accurate than analog spring scales. For best accuracy, place scales on a hard flat surface, calibrate regularly, and weigh items at room temperature. Professional laboratory balances can measure to 0.0001 grams. When converting between units, the math is exact, but the measurement itself always has some uncertainty.
Why is the kilogram the SI base unit of mass?
The kilogram was redefined in 2019 based on the Planck constant, making it independent of any physical artifact. Previously, it was defined by a platinum-iridium cylinder kept in Paris since 1889. The kilogram is the only SI base unit with a prefix (kilo-) in its name, a historical quirk from the French Revolution when the gram was too small for practical commerce. All other mass units in the SI system are derived from the kilogram: 1 milligram = 0.000001 kg, 1 metric ton = 1000 kg.
What is the difference between mass and weight?
Mass is the amount of matter in an object and is what the kilogram measures; it does not change with location. Weight is the gravitational force acting on that mass, measured in newtons, and equals mass times the local gravitational acceleration, with the standard value taken as 9.80665 metres per second squared. Everyday scales report kilograms because they are calibrated assuming Earth surface gravity, which is why the two words get used loosely.
How do I convert pounds and ounces into a single kilogram figure?
Turn the ounces into a decimal fraction of a pound by dividing by 16, add that to the whole pounds, then multiply by 0.45359237. For 8 lb 6 oz, six ounces is 0.375 lb, giving 8.375 lb, and 8.375 x 0.45359237 = 3.799 kg. The common mistake is treating the ounce figure as a decimal directly, which would give 8.6 lb and an answer about 0.10 kg too high.
How many pounds are in a stone and where is that unit used?
One stone is exactly 14 pounds, which is 6.35029318 kg. It remains in everyday use for body weight in the United Kingdom and Ireland, where a figure is spoken as stones and pounds, such as 11 stone 4 pounds. To convert, multiply the stones by 14, add the loose pounds, then apply the pound-to-kilogram factor. Very few other contexts use the stone at all.
What is the difference between a metric tonne, a short ton and a long ton?
A metric tonne is exactly 1000 kg by definition. The US short ton is 2000 pounds, which works out at 907.18474 kg, and the imperial long ton is 2240 pounds, or 1016.0469 kg. The three differ by roughly ten percent from one another, so freight, scrap and bulk-commodity figures should always name which ton is meant before any conversion to kilograms.
Why does the same object read differently on two scales?
Calibration drift is the usual cause, followed by the surface the scale sits on, since a soft or uneven floor changes how the load reaches the cells. Local gravity also varies slightly with latitude and altitude, which affects a spring-based device but not a balance comparing against reference masses. Temperature drift and the display resolution add further spread, so agreement within the stated tolerance is the realistic expectation.
How do I convert grams to kilograms without losing precision?
Divide by exactly 1000, which only moves the decimal point three places and introduces no rounding of its own. The precision loss comes afterwards, when the result is truncated for display: 1,234 g is 1.234 kg, but rounding to one decimal makes it 1.2 kg and discards 34 g. Carry the full value through any chained calculation and round only at the final step.
References
Background & Theory
1 pound = 0.45359237 kilograms exactly, 1 ounce = 0.028349523125 kg, and 1 stone = 6.35029318 kg. All three terminate because they descend from a single definition, the international avoirdupois pound fixed at exactly 0.45359237 kg in 1959.
Conversion reference table
| Conversion | Equivalent | Exact or rounded? |
|---|---|---|
| 1 pound | 0.45359237 kilograms | Exact by definition |
| 1 ounce | 0.028349523125 kilograms | Exact (1/16 lb) |
| 1 stone | 6.35029318 kilograms | Exact (14 lb) |
| 1 short ton (US) | 907.18474 kilograms | Exact (2,000 lb) |
| 1 long ton (imperial) | 1,016.0469088 kilograms | Exact (2,240 lb) |
| 1 tonne | 1,000 kilograms = 2,204.62262 pounds | Exact / derived |
| 1 grain | 0.00006479891 kilograms | Exact |
The three tons differ by more than ten percent between the lightest and the heaviest, so a shipping or scrap contract that says only "ton" is genuinely ambiguous and should be read against the jurisdiction. The kilogram has been defined since May 2019 by fixing the Planck constant at exactly 6.62607015 x 10 to the -34 joule seconds, which retired the platinum-iridium prototype in Sevres and made the kilogram reproducible in any suitably equipped laboratory.
Reviewed for accuracy by Manoj Kumar, Mathematics Educator · Editorial policy
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