Weight Converter
Convert weight (mass) between everyday units like kilograms, pounds, ounces, grams, milligrams, stone, and tons—fast, clearly, and with a step-by-step breakdown. While “weight” and “mass” are used interchangeably in daily conversation, the units here are standard mass units used for cooking, fitness tracking, shipping labels, science class, and travel baggage.
Use the calculator below to switch from kg to lb, oz to g, stone to kg, or even larger units like metric tons and US/Imperial tons. Explore more tools from our All Calculators directory, or browse the Conversion Tools category for quick unit conversions across different measurement types.
Choose a precision level (0–6 decimals) for tidy rounding, optionally show a lightweight table of additional conversions, and copy results in one tap. For health-related tracking (like bodyweight goals), you can also check the Health & Fitness hub for helpful calculators.
Convert between weight units
Enter a weight, pick a “From” unit and “To” unit, then calculate. Internally, conversions use kilograms as the base unit for consistent accuracy: your value is first converted to kg, then converted from kg to the target unit. Negative values are blocked to avoid confusing outputs for typical weight use cases.
How it works
This Weight Converter uses a simple, reliable approach: every unit is represented as a factor relative to kilograms (kg). That means each unit has a “how many kilograms in 1 unit” value. For example, 1 pound (lb) equals 0.45359237 kilograms, and 1 gram (g) equals 0.001 kilograms. With these factors, any unit can convert to any other without guesswork.
The core idea is a two-step conversion. First, convert the input into kilograms (the base). Second, convert from kilograms to your target unit. This is the same approach used in many professional conversion tables, because it avoids unit-to-unit shortcut formulas that can introduce mistakes when expanded to many units.
Variables and formula
Let x be your entered value, f be the kg factor of the “From unit,” and t be the kg factor of the “To unit.” Then:
- Value in kg =
x × f - Converted output =
(x × f) ÷ t
Practical note: people often say “weight” when they mean “mass.” In everyday contexts (bodyweight, ingredient amounts, parcel labels), these units are treated as mass units. The calculator keeps it practical by focusing on standard conversion factors and clear rounding control.
Use cases
- Fitness tracking (kg ↔ lb): Many apps and gym scales switch between metric and imperial. Converting accurately helps you compare progress, set targets, and interpret plans that use different units.
- Cooking and baking (g ↔ oz): Recipes may list ingredients in grams while your kitchen tools show ounces. Quick conversion helps you measure more precisely—especially for flour, spices, and portions.
- Shipping and logistics (kg ↔ lb/tons): Courier rules and freight quotes often use different unit standards depending on region. Converting reliably reduces surprises in declared weight and pricing tiers.
- Travel baggage limits (kg ↔ lb): Airlines publish baggage limits in kilograms or pounds. Converting before you pack helps you avoid fees and last-minute repacking at the airport.
- Science and education (mg ↔ g ↔ kg): Lab exercises and homework often shift between milligrams, grams, and kilograms. Seeing the intermediate kg step makes the logic easy to learn and verify.
- UK & Ireland contexts (stone): Bodyweight is sometimes discussed in stone (st). Converting stone to kg or lb helps you interpret health guidance and compare across regions.
Examples
Example 1: 72.5 kg to lb
Enter 72.5, choose Kilogram (kg) → Pound (lb), and keep precision at 2 decimals. The converter first treats 72.5 kg as already in kilograms, then divides by the lb-to-kg factor (0.45359237). The result is about 159.83 lb, which is useful for comparing metric bodyweight to US-based charts.
Example 2: 12 oz to g
Enter 12, choose Ounce (oz) → Gram (g). The converter multiplies 12 by the oz factor (0.028349523125) to get kilograms, then divides by the gram factor (0.001). The output is about 340.19 g. This is a common conversion when a recipe lists ounces but a scale displays grams.
Example 3: 11 st to kg
Enter 11, choose Stone (st) → Kilogram (kg). One stone equals 6.35029318 kg, so 11 st converts to 69.85 kg (rounded to 2 decimals). This is helpful when someone reports weight in stone but you track goals in kilograms.
Common Mistakes
- Mixing up “ton” types: A metric ton (t), a US short ton, and an Imperial long ton are different values. Always choose the correct ton variant for your context.
- Rounding too early: If you round intermediate steps, you can drift from accurate results—especially when converting very small or very large values.
- Confusing oz (ounces) with fl oz (fluid ounces): Ounces here are weight (mass). Fluid ounces measure volume and need ingredient density to convert.
- Typing separators incorrectly: Use a decimal point and digits only. Commas as thousands separators can be misread depending on locale formatting rules.
- Using negative values for typical weights: Negative weights are blocked here because most real-world uses (bodyweight, packages, ingredients) are non-negative.
Quick Tips
- Use “Show all conversions” when you want a quick cross-check across multiple units without re-running separate conversions.
- Pick precision based on purpose: 0–1 decimals often fits labels and luggage; 2–4 decimals can help with science and recipe scaling.
- Sanity-check with kg: If a result seems off, look at the “In kilograms” line—kg is the base and often easiest to reason about.
- Keep the unit context in mind: Stone is common in the UK/Ireland, pounds in the US, and kilograms in most scientific and global contexts.
- Avoid unit ambiguity for tons: If you’re reading a shipping spec, it often states “short ton” or “long ton.” Match that exactly.
FAQ
What’s the difference between weight and mass in this converter?
In everyday life, people usually say “weight” when they mean “mass,” especially for bodyweight, ingredient amounts, and package labels. Technically, mass is the amount of matter and weight is the force due to gravity. The units in this converter (kg, lb, oz, g, mg, stone, and tons) are commonly treated as mass units in practical contexts, so the converter focuses on standard unit factors. For typical household, fitness, and shipping use, this is exactly what you need. If you’re doing physics force calculations, you’d also need gravity and newtons, which is a different type of conversion.
Why does the calculator convert through kilograms (kg) first?
Converting through kilograms provides a consistent base that reduces mistakes and keeps the logic scalable. Instead of maintaining separate formulas for every possible pair of units, each unit only needs a single factor relative to kg. The converter first converts your input to kg using the “From” factor, then converts from kg to the target using the “To” factor. This approach is reliable for small units (mg) and large units (tons) alike, and it avoids the pitfalls of chained shortcuts. It also makes the step-by-step breakdown easy to follow and verify.
How accurate are the pound (lb) and ounce (oz) conversions?
The converter uses standard definitions for imperial units commonly referenced in measurement tables: 1 lb equals 0.45359237 kg, and 1 oz equals 0.028349523125 kg. These values are widely used and provide very high accuracy for everyday needs like recipes, packaging, and fitness tracking. Your displayed result is rounded to your chosen precision, but the internal computation keeps full floating-point precision before rounding. If you need extremely strict accounting or lab-grade documentation, you should match the rounding and reporting rules required by your organization, but the underlying factors here are solid for general conversion.
Can I convert stone (st) to kilograms or pounds?
Yes. Stone is often used for bodyweight in the UK and Ireland, and it converts cleanly to kg or lb. The converter treats 1 stone as 6.35029318 kg, then converts from kg to whatever target unit you choose. For example, switching stone to kilograms is straightforward (multiply by the stone-to-kg factor), and switching to pounds will also work through kg automatically. If you want to compare stone values to a US chart, choose “To unit: Pound (lb).” If you track progress in metric, choose “To unit: Kilogram (kg)” and set the precision you prefer for regular weigh-ins.
What’s the difference between metric ton, US short ton, and Imperial long ton?
These “tons” are not interchangeable. A metric ton (t) equals 1000 kg and is commonly used internationally. A US ton (short ton) equals 2000 lb, which is about 907.18474 kg, and is used in many US industrial contexts. An Imperial ton (long ton) equals 2240 lb, which is about 1016.0469088 kg, and appears in some UK historical or specialized references. When converting, make sure you pick the ton that matches your source document. If a shipping quote says “short ton,” use US ton; if it says “tonne,” it typically means metric ton.
Why won’t it accept scientific notation like 1e3?
Scientific notation is powerful, but it can confuse everyday inputs and lead to accidental misreads when people copy values from spreadsheets or calculators. This converter prioritizes clarity and reduces input mistakes by accepting only standard digits and a decimal point. For most common weight conversions—bodyweight, recipe ingredients, parcels, and baggage limits—scientific notation is rarely needed. If you must convert very large or tiny numbers, enter the full value directly (within the maximum limit). This also keeps validation messages friendly and consistent for mobile users.
How does the precision setting affect the result?
Precision controls how many decimal places are shown in the displayed output and in the optional “Show all conversions” table. For example, choosing 2 decimals will display results like 159.83 lb, while choosing 0 decimals would show 160 lb. Internally, the converter calculates using full floating-point precision and only rounds at the end for display. This helps maintain accuracy, especially when converting between small units like mg and larger units like kg. If you’re labeling packages, fewer decimals often look cleaner; for science or detailed recipes, more decimals can be helpful.
Is this converter private and does it send my data anywhere?
The calculator runs locally in your browser and performs conversions on the page without sending your inputs to a server. That means you can convert personal values like bodyweight or business values like shipment weights without uploading them through the tool itself. Copy actions are handled using your device’s clipboard features (when available) or a fallback method that stays on the page. As always, if you paste results into another app, that app’s privacy rules apply. The “Last Updated” line is a static page note and does not reflect any tracking.
What should I do if my result looks wrong?
First, check that you selected the correct “From” and “To” units—mix-ups (like choosing US ton vs metric ton) are a common source of confusion. Next, look at the “In kilograms” line: since kg is the base, it’s a great sanity check. If your kg value seems unreasonable, your input or “From unit” is likely incorrect. Also consider precision: if you choose 0 decimals, small differences can disappear due to rounding. Finally, use “Show all conversions” to compare across units and catch mismatches (for example, grams vs milligrams differ by a factor of 1000).
Sources & References
The following references are commonly used for general unit definitions and conversion factors:
- International Bureau of Weights and Measures (BIPM) — SI unit framework and definitions
- NIST (National Institute of Standards and Technology) — measurement references and unit guidance
- UK Weights and Measures conventions — common imperial unit relationships (stone, long ton)
- General engineering conversion tables for metric and imperial mass units
Trust / E-E-A-T
Accuracy & method
Conversions are performed using fixed factors relative to kilograms (kg) and the two-step method shown in the breakdown. Everything runs locally in your browser. No external libraries are loaded, and results are generated instantly after validation.
Rounding / precision policy
The precision dropdown controls only display rounding. Internally, calculations keep full floating-point precision until the final formatted output. For very large inputs (over 1e12) the calculator will show a friendly message and skip animations to keep the experience stable.
Privacy-first
Inputs stay on your device. Copy buttons place plain text on your clipboard (when supported) so you can paste results into notes, emails, or spreadsheets. No values are transmitted by the converter itself.
Last Updated: January 17, 2026