To convert pounds to kilograms, multiply by 0.4536. To convert kilograms to pounds, multiply by 2.205. A 180-pound person weighs 81.6 kg. To convert ounces to grams, multiply by 28.35. Weight conversions come up constantly: international food labels, medical records, shipping limits, and cooking recipes all switch between imperial and metric units.
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What Is a Weight Converter?
A weight converter is a tool that converts a measurement in one weight or mass unit into all other common units simultaneously. Enter a value in pounds and instantly see the equivalent in kilograms, ounces, grams, stone, metric tonnes, and US tons — no need to look up conversion factors or do the math manually.
Weight conversions are needed in everyday life more often than most people realize. US recipes use ounces and pounds; European and Asian recipes use grams and kilograms. Medical records in the US use pounds; records from most other countries use kilograms. Airline baggage allowances are published in both pounds (US domestic) and kilograms (international). Shipping weight limits, gym equipment, nutritional labels, and product specifications all require fluency across both systems.
The two main systems are the imperial system (pounds, ounces, stone) used primarily in the US and UK, and the metric system (grams, kilograms, metric tonnes) used in most of the world and in all scientific contexts. The exact conversion factor between them has been fixed by international agreement since 1959: 1 pound = 0.45359237 kilograms exactly.
A weight converter also handles the less common units: milligrams and micrograms for medication dosing; troy ounces for precious metals (one troy ounce = 31.1 grams, about 10% heavier than a standard ounce); stone for UK body weight (1 stone = 14 pounds); and both short tons (US) and metric tonnes for industrial and shipping use.
How to Use the Weight Converter
- Enter the value. The weight or mass amount you want to convert.
- Select the source unit. Pound, kilogram, ounce, gram, stone, ton, milligram, etc.
- Read all conversions. All common units displayed simultaneously — no need to convert one at a time.
The converter handles both small-scale conversions (milligrams for medication, grams for cooking) and large-scale conversions (tons, metric tonnes for shipping and industrial use).
Key Weight Conversion Factors
| From | To | Multiply By | |------|-----|------------| | Pounds (lb) | Kilograms (kg) | × 0.4536 | | Kilograms (kg) | Pounds (lb) | × 2.2046 | | Ounces (oz) | Grams (g) | × 28.3495 | | Grams (g) | Ounces (oz) | × 0.03527 | | Stone (st) | Pounds (lb) | × 14 | | Stone (st) | Kilograms | × 6.3503 | | US Tons (short) | Kilograms | × 907.185 | | Metric Tonnes | Kilograms | × 1,000 | | Milligrams (mg) | Grams (g) | ÷ 1,000 | | Micrograms (μg) | Milligrams (mg) | ÷ 1,000 |
Exact definitions:
- 1 lb = 0.45359237 kg (exact by international agreement since 1959)
- 1 oz = 28.349523... g
- 1 kg = 2.20462... lbs
- 1 gram = 1,000 milligrams
Common Weight Conversions
Body weight:
| Pounds | Kilograms | |--------|-----------| | 100 | 45.4 | | 120 | 54.4 | | 150 | 68.0 | | 180 | 81.6 | | 200 | 90.7 | | 250 | 113.4 |
Cooking/food:
| Ounces | Grams | |--------|-------| | 1 oz | 28.3 g | | 4 oz (quarter pound) | 113.4 g | | 8 oz (half pound) | 226.8 g | | 16 oz (1 pound) | 453.6 g | | 3.5 oz | 100 g |
Stone: The UK Weight Unit
In the United Kingdom, body weight is often expressed in stone and pounds. 1 stone = 14 pounds. A person weighing 11 stone 6 pounds weighs: (11 × 14) + 6 = 154 + 6 = 160 pounds = 72.6 kg.
| Stone | Pounds | Kilograms | |-------|--------|-----------| | 8 st | 112 lb | 50.8 kg | | 10 st | 140 lb | 63.5 kg | | 12 st | 168 lb | 76.2 kg | | 14 st | 196 lb | 88.9 kg |
Frequently Asked Questions
What is the difference between weight and mass? Technically: mass is the amount of matter in an object (measured in kilograms); weight is the gravitational force acting on that mass (measured in newtons). In everyday usage, the terms are used interchangeably because we measure weight on Earth under approximately constant gravity. You would weigh about 1/6 of your Earth weight on the Moon (where gravity is 1/6 of Earth's), but your mass would be the same everywhere. When people say they "weigh 80 kg," they technically mean their mass is 80 kg.
What is a troy ounce vs. a regular ounce? A regular (avoirdupois) ounce = 28.3495 grams. A troy ounce = 31.1035 grams — about 10% heavier. Gold, silver, platinum, and other precious metals are measured in troy ounces. When you see "gold at $2,000/oz," that is $2,000 per troy ounce. A "pound" of gold is 12 troy ounces (373.2 g), while a "pound" of everything else is 16 regular ounces (453.6 g) — another reason precious metal weights need clarification.
How is luggage weight measured at airports? US domestic airlines typically use pounds; international airlines and most non-US airlines use kilograms. Standard checked baggage limits: 50 lbs (23 kg) for US domestic; 23 kg (50.7 lbs) for most international. Carry-on limits range from 7 kg (15 lbs) to 10 kg (22 lbs) depending on airline. Overweight fees are expensive ($50–200+ per bag) — always weigh baggage at home using a scale before departure.
What is a metric tonne vs. a US ton? 1 metric tonne = 1,000 kg = 2,204.6 lbs. 1 US ton (short ton) = 2,000 lbs = 907.2 kg. 1 UK ton (long ton) = 2,240 lbs = 1,016 kg. The metric tonne is the international standard in most scientific, commercial, and industrial contexts. The US "ton" is typically used in the US for commodities, trucking, and informal usage. When reading about global trade, shipping, or commodities, "tonne" usually means the metric version (1,000 kg).
How do I convert between different medication dosage units? Medications use metric mass units: 1 gram = 1,000 milligrams (mg) = 1,000,000 micrograms (mcg/μg). For example: 500 mg Tylenol = 0.5 g Tylenol. 0.25 mg warfarin = 250 mcg. Be extremely careful with medication conversions — errors between mg and mcg (1,000× difference) can be life-threatening. Always verify with a pharmacist when in doubt.
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Convert Weight Now
The free Weight Converter at RoughTools converts between pounds, kilograms, ounces, grams, stone, and other weight units. Enter one value to see all conversions at once. No account needed, completely free.