The exact conversion factors for kilograms, pounds, grams, ounces, and stone, with quick-reference tables and worked examples for body weight, cooking, and shipping.
Published September 6, 2026 · Reviewed by the Ihsabha Editorial Team
Weight and mass conversion comes up constantly — checking your weight on a scale calibrated in the "wrong" unit, converting a recipe's grams into ounces or cups, figuring out a shipping package's billable weight, or reading a nutrition label from another country. Because the metric system (grams, kilograms) and the imperial/US customary system (ounces, pounds, stone) use completely different base units with no clean round-number relationship between them, converting by hand requires either a memorized factor or a quick calculation. This guide covers the exact conversion factors, the formulas behind them, and enough worked examples to make weight conversion fast and error-free.
The metric system measures mass in grams and kilograms, scaling cleanly by factors of 1,000 — 1 kilogram equals 1,000 grams, and 1 metric tonne equals 1,000 kilograms. It's the standard system used for scientific work, most of the world's body-weight measurements, and virtually all nutrition labeling outside the United States. The imperial and US customary systems instead use ounces, pounds, and stone, where 1 pound equals 16 ounces and, in the UK, 1 stone equals 14 pounds — none of which line up with round metric numbers. This mismatch is exactly why weight conversion needs either a memorized factor or a tool; Ihsabha's Unit Converter handles the calculation instantly in either direction if you'd rather skip the manual math. You can find a fuller explanation of this specific point in How to Calculate Percentage Error: Formula, Steps & Worked Examples. Use the Unit Converter below to check your own numbers quickly and accurately.
These factors cover the overwhelming majority of everyday weight and mass conversions:
Unlike some length conversions, none of these weight factors are perfectly round numbers by international definition — the kilogram-to-pound relationship in particular is a repeating decimal in practice, which is why 2.20462 is a rounded, practical value rather than an exact one, though it's precise enough for virtually any everyday or professional use.
This is the single most searched weight conversion, largely because of body weight. Worked examples:
For body-weight tracking specifically, small rounding differences rarely matter day to day, but for medical dosing, shipping cost calculations, or competitive sports with strict weight classes, using the full 2.20462 factor rather than a rough estimate avoids compounding errors.
Grams and ounces are the units most often used in cooking and small-item shipping. Worked examples:
Kitchen scales that toggle between grams and ounces use exactly this factor internally, but when a recipe from a different region lists an ingredient purely in ounces or purely in grams and your scale only supports one unit, converting manually with 28.3495 gives you the same precision the scale would.
For conversions people look up most often, a table saves recalculating each time:
| From | To | Multiply By |
|---|---|---|
| Kilograms | Pounds | 2.20462 |
| Pounds | Kilograms | 0.453592 |
| Grams | Ounces | 0.035274 |
| Ounces | Grams | 28.3495 |
| Stone | Kilograms | 6.35029 |
| Stone | Pounds | 14 |
| Pounds | Ounces | 16 |
Stone is a unit still commonly used for body weight in the United Kingdom and Ireland, though rarely seen elsewhere. One stone always equals exactly 14 pounds, so converting stone requires a two-step process when the target unit is kilograms:
Body weight in the UK is often expressed as a combination, like "11 stone 6 pounds" rather than a single decimal stone value — in that case, convert the pounds portion separately and add it: (11 × 14) + 6 = 160 total pounds, then multiply by 0.453592 to reach 72.57 kg.
The newborn-weight example follows the same two-step pattern as the height conversions covered in Ihsabha's length conversion guide — convert to a single decimal unit first, then split the fractional remainder into the smaller unit (ounces here, inches there).
In everyday language, "weight" and "mass" are used interchangeably, and for virtually all daily purposes on Earth that's perfectly fine. Scientifically, however, they're different quantities: mass is the amount of matter an object contains and never changes regardless of location, while weight is the force gravity exerts on that mass, measured in units like newtons in physics, and it does change with gravity — an object's mass on the Moon is identical to its mass on Earth, but its weight (as a force) is roughly one-sixth as much because lunar gravity is weaker. Kilograms and pounds are, strictly speaking, units of mass, though "pound-force" also exists as a distinct unit in physics and engineering contexts. For everyday conversions — body weight, cooking, shipping — this distinction rarely matters, but it's worth knowing it exists if you ever encounter weight expressed in newtons.
The pound traces back to Roman times, derived from the "libra" — which is exactly why the abbreviation for pound is "lb" rather than a letter from the word "pound" itself. Over the following centuries, different regions of Britain used pounds of varying sizes (a "troy pound" for precious metals, an "avoirdupois pound" for general goods), and it wasn't until the avoirdupois pound was standardized in the 19th century that "the pound" settled into the roughly 453.6-gram unit used today. The kilogram, by contrast, is a much younger and more deliberately engineered unit, introduced during the same French Revolutionary reforms that produced the meter, originally defined as the mass of one liter of water at its most dense temperature. Since 2019, the kilogram has been redefined using a fixed value of the Planck constant rather than a physical reference object, making it one of the most precisely defined units in all of science — a far cry from its origins as a practical wartime standard for trade and taxation.
Air travel is one of the most common places people run into weight conversion under pressure, since baggage allowances are set differently by airline and region — many international carriers list checked-bag limits in kilograms (commonly 20 kg or 23 kg for economy class), while US domestic carriers typically use pounds (commonly a 50 lb limit). Knowing that 23 kg converts to roughly 50.7 lbs makes it easy to compare an unfamiliar kilogram limit against a more familiar pound figure without needing a scale at hand. International shipping and customs forms present the same challenge in reverse — a package weighed on a US postal scale in pounds and ounces often needs to be declared in kilograms and grams for an international customs form, and getting this conversion wrong can lead to under- or over-estimating shipping costs, since many carriers price by weight brackets rather than a smooth continuous scale. You can use the Unit Converter to get the result instantly, with no manual math.
Weightlifting and strength sports mix unit systems constantly, since Olympic weightlifting and most of international sport uses kilograms, while US gyms and equipment are frequently labeled in pounds. Standard weight plates in US gyms typically come in 45, 35, 25, 10, 5, and 2.5 lb increments, while international and Olympic-standard plates use 25, 20, 15, 10, 5, and 2.5 kg increments — which means a lifter moving between a US gym and an international competition setting needs to reconstruct their working weights in the other system rather than just eyeballing an equivalent plate. A common reference point: a 225 lb bench press (a popular US strength-training milestone, "two plates") converts to 225 × 0.453592 = 102.06 kg, just over the psychologically significant 100 kg mark used as a comparable milestone internationally.
A handful of recurring errors account for most incorrect weight conversions:
Baking in particular is sensitive to weight accuracy because ingredient ratios affect texture and rise in ways that volume measurements (cups, tablespoons) can't always capture consistently — a cup of flour can vary by dozens of grams depending on how it's packed, but 120 grams of flour is always exactly 120 grams. This is why many baking recipes, especially those from regions using the metric system, list ingredients by weight in grams rather than by volume, and why converting those gram measurements accurately into ounces (or vice versa) matters more for baking than for most other cooking. For recipes that mix weight and volume measurements, Ihsabha's Cooking Measurement Converter handles both unit types together.
Skip the manual arithmetic. Ihsabha's Unit Converter handles weight and mass conversions between kilograms, grams, pounds, and ounces instantly and accurately, with no rounding guesswork.
Nutrition labels and grocery packaging are another everyday source of weight conversion, especially for anyone comparing products across regions or following a diet plan that specifies gram-based portions. US nutrition labels frequently list serving sizes in ounces alongside grams, while most other countries use grams exclusively, so converting a "3 oz serving" recommendation into grams (3 × 28.3495 = 85 g) makes it directly comparable to a metric-labeled product. Bulk grocery pricing adds a further layer — comparing a US product priced per pound against an imported product priced per kilogram requires converting one to the other before the prices can be compared fairly, since simply comparing the two sticker prices without converting the units would be misleading.
Before relying on a converted weight for something that matters — a shipping form, a dosage, a recipe — a few quick sanity checks help catch mistakes:
Postal and courier pricing tiers often sit at round numbers in one unit system but not the other, which can make a shipment unexpectedly cross into a more expensive bracket once converted. A parcel that weighs a tidy 2 kg, for instance, converts to 4.41 lbs — comfortably under a 5 lb pricing threshold — but a parcel weighing 2.3 kg converts to 5.07 lbs, just barely crossing that same threshold into a higher-priced bracket. Because of this, it's worth converting a package's actual weight precisely rather than rounding early when the result is close to a known pricing cutoff, since a seemingly small rounding shortcut can end up costing more at checkout than the few extra seconds a precise calculation would have taken.
Weight is one of several unit categories people convert regularly alongside it. If your calculation also involves room dimensions, height, or distance, Ihsabha's guide to length unit conversion covers meters, feet, inches, and miles in the same depth. And for recipes, weather, or oven temperatures, the guide to temperature conversion between Celsius, Fahrenheit, and Kelvin covers that separate conversion process step by step.
Multiply the number of kilograms by 2.20462. For example, 70 kg × 2.20462 = 154.32 lbs. To convert pounds to kilograms, multiply by 0.453592 instead.
One ounce equals approximately 28.3495 grams. To convert grams to ounces, divide by 28.3495; to convert ounces to grams, multiply by 28.3495.
One stone equals 14 pounds exactly. To convert stone to kilograms, multiply the stone value by 6.35029.
Not technically. Mass measures the amount of matter in an object and stays constant everywhere, while weight measures the force of gravity acting on that mass and changes depending on location. In everyday use on Earth, however, kilograms and pounds are used interchangeably for both.
Weight and mass conversion is exact math with a fixed conversion factor for each unit pair — the only real sources of error are applying a factor in the wrong direction or rounding too aggressively partway through a calculation. Keep the core factors from the table above on hand, watch out for the US ton vs. UK ton vs. metric tonne distinction on large weights, and converting between kilograms, pounds, grams, and ounces becomes a quick, reliable step whether you're reading a nutrition label, packing a suitcase, or following a recipe from the other side of the world.
Convert it instantly with Ihsabha's Mass & Weight Calculator and Speed Calculator.