Weight Converter
Convert between kilograms, pounds, ounces, stone, grams, and other mass units instantly. Enter a value, choose your units, and get an accurate conversion with the factor displayed.
Mass Versus Weight: They're Not the Same Thing
People use "mass" and "weight" as if they mean the same thing. In everyday conversation, nobody will correct you. But the distinction actually matters once you step outside of a grocery store. Mass is a measure of how much matter an object contains. It stays the same whether you're standing in your kitchen or floating on the International Space Station. Weight, on the other hand, is the force that gravity exerts on that mass. It changes depending on where you are.
An astronaut who masses 80 kilograms still masses 80 kilograms in orbit. But her weight up there is effectively zero because she's in freefall. Put her on the Moon, and she'd weigh about one-sixth of what she weighs on Earth—roughly 130 newtons instead of 785 newtons—even though her mass hasn't changed by a single gram.
So why does everyone, including this converter, use the terms interchangeably? Because on Earth's surface, the distinction rarely produces a practical difference. Gravity is consistent enough across the planet that 1 kilogram of mass always corresponds to about 9.81 newtons of weight. Your bathroom scale reads in kilograms or pounds, but it's technically measuring force, not mass. The conflation is harmless for cooking, shipping, or checking luggage—just don't try it in a physics exam.
The kilogram is officially a unit of mass, not weight. The International System of Units defines it using the Planck constant as of 2019, replacing the old physical prototype—a platinum-iridium cylinder stored in a vault outside Paris—that had served as the world's reference kilogram since 1889. That cylinder had been slowly gaining mass from surface contamination, which is a strange problem to have when your job is to define what a kilogram means.
How the Metric System Took Over (Almost) Everywhere
The kilogram and gram emerged from the same revolutionary French project that produced the meter. The original kilogram was defined in 1795 as the mass of one cubic decimeter of water at its maximum density—roughly 4 degrees Celsius. That definition tied mass to length and volume in a neat, logical package that made the metric system feel internally consistent. A liter of water weighed a kilogram. A milliliter weighed a gram. Everything connected.
Adoption spread slowly at first. France mandated metric units in 1840 after decades of public resistance—people kept using the old measures in markets and workshops regardless of what the law said. But industrialization changed the calculus. International trade required shared standards, and metric offered the cleanest option. The Treaty of the Metre in 1875 brought 17 nations together to formalize the system, and the count has grown to over 60 signatories since.
Today, only three countries have not officially adopted the metric system as their standard: the United States, Myanmar, and Liberia. Even so, metric is used within these countries for science, medicine, and certain industries. American pharmacists measure medications in milligrams. Car mechanics work with liters and millimeters. The military switched to metric maps decades ago.
The push-and-pull between metric and imperial creates a peculiar landscape in countries like the UK, where road signs display miles, pubs serve pints, but supermarkets label produce in grams and kilograms. People there often describe their body weight in stone (an old unit equal to 14 pounds) while buying steak by the kilogram. It's a cultural hybrid that somehow works, even if it makes no systematic sense.
Stone and Pounds: The British Way of Weighing People
If you've ever watched a British television show where someone mentions they weigh "eleven stone four," that might have sounded like a foreign language. Stone is an old English unit equal to 14 pounds, or about 6.35 kilograms. It was originally used for weighing commodities—wool, cheese, and grain—and the exact weight of a stone varied by commodity and region until Parliament standardized it at 14 pounds in 1835.
The British still use stone for body weight even though the UK officially adopted the metric system. Ask someone in London how much they weigh and you'll almost certainly hear an answer in stone and pounds. Ask them how much flour to buy for a recipe and they'll switch to grams without blinking. This selective attachment to old units isn't unique to Britain—Americans do the same thing with Fahrenheit and miles—but stone is unusual because it's genuinely unknown in most other English-speaking countries outside the UK and Ireland.
Converting between stone, pounds, and kilograms is straightforward once you know the anchors. One stone is 14 pounds, so 10 stone is 140 pounds. A person who weighs 12 stone 7 pounds weighs (12 × 14) + 7 = 175 pounds, or about 79.4 kilograms. Going the other direction, divide your weight in pounds by 14 to get stone. A 185-pound person is 13 stone 3 pounds (185 ÷ 14 = 13 remainder 3).
The stone unit shows up occasionally in American horse racing, where jockeys' weights were historically reported in stone, and in some older medical literature. Outside those niches, it's essentially a British cultural artifact—one that persists not because it's better than kilograms or pounds, but because habits formed in childhood tend to stick around for life.
Weight Conversions in the Kitchen
Cooking is where weight conversions cause the most day-to-day frustration, especially when you're working from a recipe written for a different measurement system. American recipes specify ingredients by volume—cups, tablespoons, teaspoons—while European and professional recipes use weight in grams. The problem is that volume measurements for dry ingredients are unreliable. A cup of flour can weigh anywhere from 120 grams to 160 grams depending on whether it's sifted, spooned, or scooped.
That variability is why serious bakers weigh everything. A recipe calling for 250 grams of all-purpose flour will produce the same result every single time, regardless of how the flour is stored or handled. Volume measurements introduce a margin of error that's fine for casual cooking but can wreck pastry, where ratios of flour to fat to liquid need to be precise.
The most common kitchen weight conversions: 1 ounce is about 28.35 grams. A quarter-pound stick of butter is 113 grams. A pound of sugar is 454 grams. Most kitchen scales toggle between ounces and grams with a button press, which eliminates mental math entirely. If you bake regularly and don't own a kitchen scale, buying one for $15 will improve your results more than any other single equipment upgrade.
Spices create a different conversion challenge. Recipes often call for teaspoons of ground spices, but spice weight varies enormously by type. A teaspoon of ground cinnamon weighs about 2.6 grams, while a teaspoon of ground cloves weighs roughly 3.5 grams. When scaling recipes up for large batches—say, you're making five times the normal quantity of a spice blend—weighing each spice eliminates the compounding errors that come from repeatedly measuring small volumes. Any experienced caterer or commercial kitchen worker will tell you the same thing: scales beat spoons.
Weight Conversion Formula
Converted Value = Input Value × (Source Unit in Kilograms / Target Unit in Kilograms)
All mass units can be expressed as a number of kilograms. To convert between any two units, the input value is multiplied by the source unit's kilogram equivalent and then divided by the target unit's kilogram equivalent. For example, 1 pound equals 0.453592 kilograms and 1 ounce equals 0.0283495 kilograms. Converting 150 pounds to kilograms means multiplying 150 by 0.453592, which gives 68.039 kilograms. Key conversion factors to know: 1 lb = 0.453592 kg, 1 stone = 6.35029 kg (or 14 pounds), 1 metric ton = 1,000 kg, 1 US short ton = 907.185 kg, and 1 imperial long ton = 1,016.05 kg.
Where:
- Input Value = The numeric quantity being converted
- Source Unit in Kilograms = How many kilograms one unit of the source measurement equals (e.g., 1 pound = 0.453592 kg)
- Target Unit in Kilograms = How many kilograms one unit of the target measurement equals (e.g., 1 kilogram = 1.0 kg)
Example Calculations
Body Weight Conversion
Converting a body weight of 150 pounds to kilograms for a medical form.
A weight of 150 pounds converts to kilograms by multiplying by 0.453592 (since 1 lb = 0.453592 kg). The result is 150 × 0.453592 = 68.039 kg. This conversion is commonly needed when filling out medical forms or fitness tracking apps that use metric units. For a quick mental estimate, dividing pounds by 2.2 gives a close approximation—150 / 2.2 = 68.18 kg.
Shipping Cargo Weight
Converting a shipment weight from metric tons to US short tons for a freight quote.
International shipping often requires conversion between metric tons (1,000 kg each) and US short tons (2,000 pounds or 907.185 kg each). A 24 metric ton container converts to US tons by multiplying by 1.10231, giving 26.455 short tons. The difference matters for freight pricing because trucking quotes in the U.S. are typically calculated per short ton, while international cargo manifests use metric tons.
Frequently Asked Questions
One kilogram equals approximately 2.20462 pounds. For quick mental math, multiplying kilograms by 2.2 gives a close enough estimate for most practical purposes. The exact factor is 2.2046226218, but the rounded version works fine for everyday conversions like body weight, groceries, or luggage. Going the other direction, one pound equals 0.453592 kilograms, so dividing pounds by 2.2 approximates the kilogram value.
A US ton (also called a short ton) is 2,000 pounds, or about 907.185 kilograms. A metric ton (also called a tonne and spelled that way in many countries) is exactly 1,000 kilograms, or about 2,204.62 pounds. The metric ton is roughly 10% heavier than the US ton. There is also an imperial ton (long ton) used historically in Britain, which equals 2,240 pounds or about 1,016.05 kilograms. In international trade and shipping, the metric ton is the standard, while the short ton is primarily used in the United States.
Stone has been used in England for weighing goods since the 14th century, and it became culturally ingrained for measuring body weight long before metrication. When the UK officially adopted the metric system in the 1960s and 1970s, body weight was one area where the older unit simply refused to die out. People had grown up hearing their parents say "ten stone" and continued the habit. British media, health publications, and casual conversation still default to stone and pounds for personal weight, even as kilograms are used for virtually everything else in shops and industry.
Multiply the number of ounces by 28.3495 to get grams. For a rough estimate, multiplying by 28 is close enough for most recipes. Common benchmarks: 1 ounce is about 28 grams, 4 ounces (a quarter pound) is about 113 grams, 8 ounces (half a pound) is about 227 grams, and 16 ounces (one pound) is about 454 grams. If your recipe calls for 6 ounces of chocolate, that's approximately 170 grams. A digital kitchen scale that displays both ounces and grams makes these conversions trivial.
They weigh exactly the same—one kilogram. This old riddle works because people instinctively think about volume rather than mass. A kilogram of feathers takes up an enormous amount of space compared to a kilogram of steel, so the mental image makes feathers seem lighter. But a kilogram is a kilogram regardless of what material you're weighing. The density differs (steel is about 7,800 kg per cubic meter, while loose feathers are roughly 2.5 kg per cubic meter), which means you'd need over 3,000 times as much volume of feathers to reach the same mass as a compact block of steel.