Weight Converter

Kilograms, Pounds, Stone — Why Three Systems Still Coexist

Unlike most measurement topics where one system has largely won out, weight uses three actively competing frameworks in everyday life. The metric kilogram dominates science, medicine, and international trade. The avoirdupois pound rules American consumer culture — grocery stores, recipes, gym equipment, and body weight discussions. And stone — a unit equal to 14 pounds — persists in British and Irish conversation for describing human body weight, even among people who otherwise use metric. The result is that weight conversion remains a genuine daily need for a huge number of people, not just a niche engineering task. This tool covers all three frameworks plus pharmaceutical-grade units (milligrams, micrograms) and bulk trade units (metric ton, short ton, long ton).

Mass vs Weight: The Distinction That Matters

Strictly speaking, mass and weight are different physical quantities. Mass is the measure of how much matter an object contains, expressed in kilograms. Weight is the gravitational force acting on that mass, expressed in newtons. A 70 kg astronaut has the same mass on Earth and the Moon, but weighs about six times less on the Moon because of lower gravity. In everyday commerce, medicine, and cooking, however, everyone uses "weight" to mean mass — and all the units in this converter (kg, lbs, grams, ounces) are units of mass. If you genuinely need to work in newtons, that is a force converter, not this tool. For the overwhelming majority of real-world needs, the units here are exactly right.

Where Each Unit Is Actually Used

• Kilogram (kg): The global default for body weight outside the US and UK, grocery quantities, and packaged goods worldwide
• Gram (g): Kitchen recipes, postal parcels under 1 kg, jewellery, nutrition labels
• Milligram (mg): Drug dosages, supplement quantities, chemical reagents
• Microgram (µg): Pharmaceutical trace amounts, airborne particulate measurements (PM2.5), lab assay results
• Pound (lb): US body weight, American recipes, US shipping rates, gym weights
• Ounce (oz): US food portions, postal weight for letters and small packets, deli counter portions
• Stone (st): British and Irish informal body weight discussions; NHS patient records often record in both stone and kg
• Metric Ton (t): Industrial bulk — steel, grain, coal, cement; international commodity pricing
• Short Ton (US ton): American construction materials, recycling industry, some mining specs
• Long Ton (UK ton): Royal Navy, older British engineering documents, some shipping manifests
• Carat (ct): Gemstone and diamond weight — 1 ct = 0.2 g exactly; not to be confused with gold karat purity
• Grain (gr): Ammunition propellant loads, archery arrow weights, historical pharmaceutical compounding

The Exact Conversion Factors Used

All conversions use the official international avoirdupois definitions where applicable:

• 1 pound = exactly 0.45359237 kg (international avoirdupois pound, 1959)
• 1 ounce = exactly 0.028349523125 kg (1/16 of a pound)
• 1 stone = exactly 6.35029318 kg (14 pounds by definition)
• 1 short ton = 907.18474 kg (2,000 US pounds)
• 1 long ton = 1,016.0469088 kg (2,240 UK pounds)
• 1 carat = exactly 0.0002 kg (metric carat, 200 mg)
• 1 grain = exactly 0.00006479891 kg (1/7,000 of a pound)

Practical Scenarios: When You Actually Need This

A few situations where this converter solves a real problem: You are following a French pastry recipe that lists flour in grams but your kitchen scale shows ounces — enter the gram value, read the ounce equivalent. A freight forwarder quotes you a per-kilogram rate but your goods are logged in pounds — use the converter to reconcile. You are comparing blood test results between a UK lab (mg/dL) and a European lab (mmol/L) and need intermediate conversions. Or you are checking whether a 1.5 lb dumbbell set from an American retailer matches the 0.68 kg figure in its product specs before ordering. For cooking volumes that accompany weight measurements, the Volume Converter is the right companion. For body-height alongside body-weight, use the Length Converter.

No Data Sent — Ever

Every calculation this tool performs stays in your browser. No weight value you type is logged, transmitted, or stored. The converter is a static JavaScript application — it has no backend calls and does not connect to any external service when you type. This makes it appropriate for sensitive inputs: patient body weight, confidential pharmaceutical quantities, private inventory data, or any weight measurement you would not want shared.