Weight Converter
Convert weight between pounds, kilograms, ounces, grams, milligrams, and stones.
I hit this most often when reading European product specs or nutrition labels, grams to ounces, kilograms to pounds. The stones conversion is specifically for UK body weight references, which are still common in British media even as metric becomes more standard there.
Key conversions to memorize: 1 kg ≈ 2.205 lbs. 1 lb = 453.6 grams. 1 oz = 28.35 grams. 1 stone = 14 pounds (UK body weight unit).
The US customary vs metric divide
The United States uses the avoirdupois system for everyday weight: ounces (oz), pounds (lb), and tons. The metric system, milligrams, grams, kilograms, is used in science, medicine, nutrition labeling (increasingly), and by most of the rest of the world. The conversion between the two systems is exact by definition: one pound is exactly 453.59237 grams.
Stones, a UK-specific unit
The stone (14 pounds) is a traditional British unit still used informally in the UK and Ireland for body weight. A person weighing "11 stone 4" weighs 158 pounds or 71.7 kg. While metric is technically the official standard in the UK, stones persist in everyday conversation for body weight, much as Fahrenheit persists in the US for temperatures.
Weight in cooking and nutrition
Professional cooking and nutrition work in grams for precision. A kitchen scale accurate to 1 gram costs under $15 and makes every recipe more consistent. Volume measurements (cups, tablespoons) are convenient but imprecise, a cup of flour weighs anywhere from 120 to 160 grams depending on how it's scooped. Gram-based measurements eliminate this variability entirely.
Frequently asked questions
What's the difference between weight and mass?
In everyday use, weight and mass are used interchangeably. Technically, mass is the amount of matter in an object (kilograms in SI units) and weight is the gravitational force on that mass (newtons). On Earth's surface, the distinction doesn't matter practically. On the Moon, a 70 kg person would weigh about 115 N instead of 686 N, but their mass would still be 70 kg.
Why does the US still use pounds instead of kilograms?
The US attempted metrication in the 1970s but the effort failed due to lack of mandatory requirements and public resistance. Science, medicine, and the military all use metric in the US. Everyday commerce and consumer products remain largely in customary units due to infrastructure inertia, replacing every road sign, product label, and cultural reference point is a massive coordination problem with no single forcing mechanism.