Free Online Tool
Weight & Mass Converter
Convert between kilograms, pounds, ounces, grams, and stones — instantly, in your browser, with no rounding surprises.
Used daily by nurses tracking patient weight, runners comparing race standards, home cooks scaling international recipes, and freight teams preparing customs paperwork.
Getting started
How to use this converter
Enter a value
Type any number into the input field. Decimals are welcome — try something like 2.75 or 0.5.
Choose your units
Select the unit you're converting from (e.g. "kg") and the unit you want the result in (e.g. "lbs"). The conversion fires as you type — no button press needed.
Read your result
The result appears immediately, with up to 6 decimal places. Copy it, or keep adjusting your input.
Quick reference
Common conversion factors
Bookmark this table — these are the exact multipliers the converter uses.
| From | To | Factor | |
|---|---|---|---|
| 1 kilogram | → | 2.20462 pounds | × 2.20462 |
| 1 pound | → | 0.45359 kilograms | × 0.453592 |
| 1 ounce | → | 28.3495 grams | × 28.3495 |
| 1 gram | → | 0.03527 ounces | × 0.035274 |
| 1 stone | → | 6.35029 kilograms | × 6.35029 |
| 1 stone | → | 14 pounds | × 14 (exact) |
| 1 metric ton | → | 1,000 kilograms | × 1000 (exact) |
| 1 short ton (US) | → | 907.185 kilograms | × 907.185 |
Real-world applications
Who uses this — and why
Home cooks & bakers
Most European and Japanese recipes list ingredients by weight in grams. American recipes often use cups and ounces. When you want to bake a German Schwarzbrot from a Berlin cookbook, you need grams → ounces in seconds, not a conversion table buried in an appendix.
Example: 250 g flour = 8.82 oz
Athletes & fitness
Strength training equipment in the US uses pounds; Olympic lifting, physique competitions, and most international meets use kilograms. Knowing your one-rep max in both systems matters when traveling, competing abroad, or comparing with an international training partner.
Example: 185 lbs = 83.91 kg
Freight & logistics
Customs declarations in the EU require gross weight in kilograms. US domestic shipments quote lbs. Carriers often publish rate cards in one system, while clients invoice in another. A quick conversion at the warehouse saves costly rounding errors on multi-pallet shipments.
Example: 5,000 lbs = 2,267.96 kg
Healthcare & nursing
Drug dosages are almost always calculated per kilogram of body weight. Patients in the UK and US often know their weight only in stones and pounds. Nurses and pharmacists convert at intake — a mental math mistake here is a clinical risk, so a reliable tool matters.
Example: 12 st 4 lbs = 78.02 kg
Travel & checked baggage
Airlines publish baggage limits in kilograms on international routes and often in pounds on US domestic legs. Packing close to the limit without a scale that speaks both languages is a gamble.
Example: 23 kg limit = 50.71 lbs
Science & education
Lab protocols from different countries mix SI and imperial units depending on their era and origin. Students converting historical data sets, or teachers building cross-curricular exercises, need accurate factors they can trust.
Example: 0.5 oz = 14.17 g
Tips & best practices
Getting accurate results every time
Use decimal points, not fractions
Enter 1.5 rather than 1½. Most digital scales display decimals, and the converter expects them. If your scale shows a fraction, convert it first: ½ = 0.5, ¼ = 0.25, ¾ = 0.75.
Stone + pounds inputs
If your weight is '11 stone 6 pounds, ' convert the full value to pounds first (11 × 14 + 6 = 160 lbs), then run the lbs → kg conversion. This avoids carrying a partial remainder through two steps.
Cooking: weigh, don't scoop
Even if you're just trying to scale a recipe, weighing dry ingredients (flour, sugar, oats) is more accurate than cups. 1 cup of flour can range from 120 g to 160 g depending on how it was scooped. Use the weight converter after you measure by weight.
Logistics: tare vs gross weight
When converting cargo weight for a customs declaration, clarify whether the figure is gross (including packaging) or net (product only). The conversion factor is the same, but mixing the two up causes declaration errors that attract fines.
Healthcare: re-measure, don't estimate
Medication dosing based on weight should always come from a fresh measurement, never a recalled number. Use the converter to check your unit, not to replace the scale.
Interpreting results
What to do with your number
A converter gives you a mathematically precise answer, but precision and practicality aren't always the same thing. Here's how to read results in context:
Cooking
Round to the nearest gram or 0.1 oz. Kitchen scales rarely resolve below 1 g, so six decimal places is noise. 113.398 g → use 113 g.
Healthcare
Keep at least two decimal places for dosing calculations. A difference of 0.1 kg can matter at pediatric doses. Always double-check with a qualified clinician.
Shipping
Round up, not down. Carriers charge for the higher weight tier if you're on the boundary. 49.97 kg → declare 50 kg.
Honest limitations
What this tool doesn't do
- No force conversion. Weight-as-force (Newtons, kilogram-force, pound-force) is a different measurement from mass. This tool handles mass only.
- No gravity correction. A 70 kg mass weighs slightly less on the Moon. This converter assumes standard Earth gravity (9.80665 m/s²), which is appropriate for every everyday use case.
- No compound units. Entering "11 st 4 lb" as a single string won't work — split it into components first (see the stone tip above).
- Floating-point limits. Values beyond approximately ±10¹⁵ grams may lose precision due to IEEE 754 arithmetic. This edge case won't affect anything you'd weigh in the real world.
FAQ
Frequently asked questions
Quick answers to the questions we hear most often.
What is the difference between weight and mass?
Mass is the amount of matter in an object, measured in kilograms or pounds. Weight is technically the gravitational force on that mass, measured in Newtons. In everyday life — groceries, gym equipment, luggage — people use 'weight' to mean mass, and this converter follows that common convention.
How many pounds are in a kilogram?
One kilogram equals 2.20462 pounds. Memorizing 2.2 gets you within 0.2% of the exact answer — good enough for most situations. For clinical or freight calculations, use the full factor.
How accurate is this converter?
All calculations use IEEE 754 double-precision arithmetic with conversion factors sourced from NIST Handbook 44. The results are accurate to at least 10 significant figures, which is more precise than any consumer scale or certified industrial scale you're likely to use.
Does this tool store or share my data?
Nothing leaves your device. The conversion logic runs entirely in JavaScript in your browser. No values are sent to a server, stored in a database, or included in analytics.
What is a stone, and who uses it?
A stone is a traditional British unit of mass equal to 14 pounds, or approximately 6.35 kilograms. It's still widely used in the UK and Ireland for body weight. You'll also encounter it in some horse-racing contexts.
Why does my bathroom scale and this converter give slightly different numbers?
Consumer bathroom scales typically have an accuracy of ±0.1–0.5 kg. If the scale rounds to the nearest 0.5 lb, a reading of 154.5 lbs is really 'somewhere between 154 and 155 lbs.' The converter is only as accurate as your input — garbage in, garbage out.
Can I convert very large weights, like cargo containers?
Yes. The converter handles any value that fits in a standard number field. A fully loaded 20-foot shipping container can be around 25,000 kg — enter that freely. Just be aware that customs declarations may have their own rounding rules.
Under the hood
How the math works
Every unit pair has a single canonical conversion factor, verified against the NIST Handbook 44 (the U.S. federal standard for weights and measures). Conversions chain through a common base — grams — rather than using direct pair-to-pair lookups. This means that converting ounces → stones, for instance, goes through grams internally, eliminating compounding rounding errors that would accumulate if each step rounded its output before passing it forward.
The display rounds to 6 significant figures for readability, but the stored value is the full IEEE 754 double-precision result (~15–17 decimal digits). If you chain conversions — say, converting a result back into the original unit — the result will round-trip correctly within the limits of floating-point arithmetic.