Weight Conversion Guide: Pounds, Kilograms, Stones, and Tons Explained
Master weight conversions with this comprehensive guide covering pounds, kilograms, stones, ounces, grams, and tons. Learn the essential formulas, understand when to use each unit, and avoid common conversion mistakes for cooking, travel, shipping, and everyday life.
Understanding Weight and Mass
Weight measurement is one of the most common conversions needed in daily life, from cooking recipes to tracking body weight to shipping packages internationally. Understanding the different weight units and how to convert between them is essential for effective communication across countries and contexts.
Weight vs Mass: What's the Difference?
While we commonly use the term "weight" in everyday language, there's a technical difference:
- Mass is the amount of matter in an object, measured in kilograms, grams, pounds, or ounces. Mass stays constant regardless of location.
- Weight is the force exerted on that mass by gravity, technically measured in newtons. Weight changes based on gravitational strength.
In everyday usage, we use "weight" to refer to mass, and that's perfectly fine. When you step on a scale, you're measuring mass (even though we call it weight). This guide uses "weight" in the common everyday sense meaning mass.
Two Main Systems
Weight is measured using two primary systems:
- Metric System: Based on powers of 10, using grams (g), kilograms (kg), and metric tons. Used by most countries worldwide.
- Imperial/US Customary System: Using ounces (oz), pounds (lbs), stones (UK), and tons. Primarily used in the United States and partially in the UK.
Metric Weight Units Explained
The metric system is the international standard for weight measurement, used in scientific research, medicine, and daily life in most countries.
The Metric Weight Hierarchy
Metric units are based on the gram (g), with prefixes indicating powers of 10:
Milligram (mg)
- 1 mg = 0.001 grams (1/1000th of a gram)
- Used for: Medications, supplements, micro-ingredients
- Example: A grain of salt weighs about 60 mg
Gram (g)
- The base unit of weight in the metric system
- Used for: Cooking ingredients, small items, food portions
- Example: A US nickel weighs 5 grams; a teaspoon of sugar is about 4 grams
Kilogram (kg)
- 1 kg = 1,000 grams
- Used for: Body weight, produce, packages, most everyday items
- Example: A liter of water weighs 1 kg; average laptop weighs 1-2 kg
- Equivalent to: 2.20462 pounds
Metric Ton (tonne)
- 1 metric ton = 1,000 kilograms = 1,000,000 grams
- Used for: Vehicles, cargo shipments, industrial materials
- Example: A small car weighs about 1-1.5 metric tons
- Equivalent to: 2,204.6 pounds or 1.102 US tons
Advantages of Metric Weight Units
- Decimal-based system – Easy to convert between units by multiplying or dividing by 10, 100, or 1000
- Universal standard – Used by 190+ countries and all scientific communities
- Simple conversions – 1 kg = 1000 g, 1 g = 1000 mg (easy to remember)
- Integrates with other metrics – Water's density makes 1 liter = 1 kg
Imperial Weight Units Explained
The imperial system is primarily used in the United States, with some units still in use in the UK. Understanding these units is essential for anyone working with American recipes, shipping to the US, or communicating with American colleagues.
Imperial Weight Units
Ounce (oz)
- 1 oz = 28.3495 grams (often rounded to 28.35 g)
- 16 ounces = 1 pound
- Used for: Cooking ingredients, food portions, small packages
- Example: A slice of bread weighs about 1 oz; a baseball weighs about 5 oz
Pound (lb or lbs)
- 1 lb = 16 ounces = 453.592 grams (often rounded to 454 g)
- 1 lb = 0.453592 kilograms (often rounded to 0.45 kg)
- Used for: Body weight (US), produce, packages, most everyday items in the US
- Example: A loaf of bread weighs about 1 lb; a laptop weighs 2-5 lbs
Stone (st)
- 1 stone = 14 pounds = 6.35029 kilograms
- Used primarily in: UK and Ireland for body weight
- Notation: Often written as "10st 5" (10 stone 5 pounds)
- Example: Average adult male weighs 11-13 stones
Ton (US and UK)
There are different types of tons - be careful which one you're using:
- US Ton (short ton): 2,000 pounds = 907.185 kg
- UK Ton (long ton): 2,240 pounds = 1,016.05 kg
- Metric Ton (tonne): 1,000 kg = 2,204.6 lbs (international standard)
- Used for: Vehicles, shipping cargo, bulk materials
Important: Ounces vs Fluid Ounces
Don't Confuse These!
- Ounces (oz) measure weight/mass – used for solid items (16 oz = 1 lb)
- Fluid ounces (fl oz) measure volume – used for liquids (different measurement entirely)
- They only match for water: 1 fl oz of water weighs approximately 1 oz, but this varies for other liquids based on density
Metric vs Imperial Weight Systems
Understanding the differences between metric and imperial weight systems helps you choose the right unit and convert accurately:
| Feature | Metric System | Imperial System |
|---|---|---|
| Base Units | Gram (g), Kilogram (kg) | Ounce (oz), Pound (lb) |
| Conversion Logic | Powers of 10 (×10, ×100, ×1000) | Mixed (16 oz = 1 lb, 14 lb = 1 stone) |
| Global Usage | 190+ countries | US (primary), UK (partial) |
| Scientific Use | Universal standard | Rarely used in science |
| Body Weight | Kilograms (most countries) | Pounds (US), Stones (UK/Ireland) |
| Cooking/Recipes | Grams (precise, preferred globally) | Ounces/Cups (common in US) |
| Shipping/Postal | Grams, Kilograms (international) | Ounces, Pounds (US domestic) |
Key Conversion Relationships
- 1 kilogram (kg) = 2.20462 pounds (lbs) ≈ 2.2 lbs
- 1 pound (lb) = 0.453592 kilograms (kg) ≈ 0.45 kg = 453.6 grams
- 1 ounce (oz) = 28.3495 grams (g) ≈ 28.35 g
- 1 gram (g) = 0.035274 ounces (oz) ≈ 0.035 oz
- 1 stone (st) = 14 pounds = 6.35029 kilograms
Essential Conversion Formulas
Master these conversion formulas to easily convert between all common weight units:
Pounds ↔ Kilograms
Pounds to Kilograms:
kg = lbs ÷ 2.2 (or lbs × 0.4536)
Kilograms to Pounds:
lbs = kg × 2.2 (or kg × 2.20462 for precision)
Examples:
- 150 lbs to kg: 150 ÷ 2.2 = 68.2 kg
- 70 kg to lbs: 70 × 2.2 = 154 lbs
Ounces ↔ Grams
Ounces to Grams:
g = oz × 28.35 (or oz × 28.3495 for precision)
Grams to Ounces:
oz = g ÷ 28.35 (or g × 0.03527)
Examples:
- 8 oz to grams: 8 × 28.35 = 226.8 g
- 250 g to oz: 250 ÷ 28.35 = 8.8 oz
Pounds ↔ Grams
Pounds to Grams:
g = lbs × 454 (or lbs × 453.592 for precision)
Grams to Pounds:
lbs = g ÷ 454 (or g × 0.0022)
Stones ↔ Pounds ↔ Kilograms
Stones to Pounds:
lbs = stones × 14
Stones to Kilograms:
kg = stones × 6.35
Pounds to Stones:
stones = lbs ÷ 14
Example: Convert 11 stone 5 to pounds and kg:
- Pounds: (11 × 14) + 5 = 154 + 5 = 159 lbs
- Kilograms: 159 ÷ 2.2 = 72.3 kg
Within Metric System
Conversions:
- Grams to Kilograms: kg = g ÷ 1000
- Kilograms to Grams: g = kg × 1000
- Milligrams to Grams: g = mg ÷ 1000
- Grams to Milligrams: mg = g × 1000
- Kilograms to Metric Tons: tonnes = kg ÷ 1000
Use Our Weight Converter
For quick and precise conversions, use our Weight Converter tool which handles all these conversions instantly, or check our Pounds to Kilograms Chart for common values.
Step-by-Step Conversion Guide
Follow this systematic approach for accurate weight conversions every time:
Step 1: Identify Your Units
Determine exactly what unit you're converting from and to. Pay special attention to:
- Ounces (weight) vs fluid ounces (volume)
- Type of ton (metric, US short ton, UK long ton)
- Whether stones include additional pounds (e.g., "11st 5")
Step 2: Choose Your Conversion Factor
Select the appropriate conversion factor:
- Quick estimates: Use rounded factors (2.2 for kg/lbs, 28 for oz/g)
- Cooking: Use rounded factors or measuring tools
- Shipping/precise work: Use full precision (2.20462 for kg/lbs, 28.3495 for oz/g)
- Scientific work: Use maximum precision available
Step 3: Perform the Calculation
Apply the conversion formula:
- Use a calculator for accuracy, especially with decimals
- Double-check whether you should multiply or divide (going from larger to smaller units = multiply, smaller to larger = divide)
- Keep extra decimal places during calculation, round at the end
Example: Convert 165 lbs to kg
165 ÷ 2.20462 = 74.84 kg
Step 4: Round Appropriately
Round based on your use case:
- Body weight: Nearest 0.1 kg or 0.5 lb
- Cooking ingredients: Nearest 5-10 g or 0.25 oz for small amounts
- Shipping: Per carrier requirements (often nearest 0.1 kg or whole oz)
- Scientific: Keep 2-3 decimal places minimum
Step 5: Verify Your Answer
Sanity check your result:
- Does the number make sense? (1 kg should be about 2.2 lbs, not 22 or 0.22)
- Is the new number larger or smaller as expected?
- Compare to known benchmarks (e.g., 100 lbs ≈ 45 kg)
- If converting body weight, is the result within typical human range? (40-150 kg or 90-330 lbs)
Quick Mental Math Tricks
For approximate conversions without a calculator:
- Pounds to Kilograms: Divide by 2, then subtract 10%
(Example: 100 lbs → 50 → subtract 5 = 45 kg, actual is 45.4 kg) - Kilograms to Pounds: Double it, then add 10%
(Example: 50 kg → 100 → add 10 = 110 lbs, actual is 110.2 lbs) - Ounces to Grams: Multiply by 30 (close enough)
(Example: 4 oz → 4 × 30 = 120 g, actual is 113.4 g)
Real-World Applications
Understanding weight conversions is essential in many everyday situations. Here's how to apply your knowledge:
Cooking and Baking
Recipe conversions are one of the most common needs for weight conversion:
- Following international recipes: European recipes use grams, American recipes use ounces or cups
- Precision baking: Weight is more accurate than volume (1 cup flour can vary by 30g depending on packing)
- Common conversions: 1 stick butter = 4 oz = 113g; 1 lb flour ≈ 454g; 8 oz sugar ≈ 225g
- Scaling recipes: Multiply all weights by the same factor (doubling recipe = multiply all ingredient weights by 2)
Body Weight and Fitness
Weight tracking varies significantly by country:
- United States: Body weight in pounds (lbs), typical adult range 120-250 lbs
- UK/Ireland: Stones and pounds (e.g., "12 stone 3"), typical range 8-18 stones
- Most other countries: Kilograms, typical adult range 55-115 kg
- Medical settings: Kilograms worldwide for dosing and BMI calculations
- Fitness tracking: Weight loss of 0.5-1 kg per week = 1-2 lbs per week
Shipping and Packages
Accurate weight is critical for shipping costs and regulations:
- US Domestic: USPS, UPS, FedEx use pounds and ounces
- International: Most carriers require kilograms
- Cost tiers: Shipping rates jump at weight thresholds (1 lb, 3 lbs, 5 lbs or 0.5 kg, 1 kg, 2 kg)
- Accuracy matters: Overestimate by 5-10% to account for packaging weight
- Air travel: Baggage limits typically 23 kg (50 lbs) or 32 kg (70 lbs)
Travel and Shopping
- Luggage limits: International flights use kg limits, domestic US flights use lbs
- Produce shopping: European markets price by kg (€2/kg), US by lb ($2/lb)
- Deli counters: "Half a pound of turkey" = "250 grams of turkey"
- Car rentals: Vehicle weight capacity in tons or kg depending on country
Scientific and Medical
- Laboratory measurements: Always use metric (mg, g, kg)
- Drug dosing: Medications dosed in mg per kg of body weight
- Nutrition labels: Serving sizes in grams with US equivalent in ounces/cups
- Research papers: Scientific publications use metric units exclusively
Pro Tip for Travelers:
Before international travel, memorize your weight in both pounds/stones and kilograms, and learn to think in the local system for shopping. "€3 per kg" is roughly "$1.35 per lb" (after conversion and typical exchange rates).
Common Mistakes to Avoid
Even experienced converters make these mistakes. Learn to avoid them:
1. Multiplying When You Should Divide
❌ Wrong:
Converting 150 lbs to kg: 150 × 2.2 = 330 kg (way too heavy!)
✓ Correct:
150 ÷ 2.2 = 68.2 kg
Remember: Pounds are larger units than kilograms, so converting from pounds to kg makes the NUMBER smaller. Think: "fewer kilograms than pounds."
2. Confusing Ounces (Weight) with Fluid Ounces (Volume)
These are completely different measurements:
- 8 oz (weight) of honey = 8 oz on a scale = 227 grams
- 8 fl oz (volume) of honey = 1 cup = about 12 oz weight = 340 grams
Always check: Is this weight (oz) or volume (fl oz)? Only water has roughly 1:1 relationship.
3. Using Wrong Type of Ton
Three different tons exist:
- Metric ton (tonne): 1,000 kg = 2,204.6 lbs
- US ton (short ton): 2,000 lbs = 907.2 kg
- UK ton (long ton): 2,240 lbs = 1,016 kg
These differ by up to 10%! Always clarify which ton is being referenced.
4. Rounding Too Early
❌ Wrong:
Converting 15 oz to kg: 15 oz → 425 g (rounded) → 0.4 kg (loses accuracy)
✓ Correct:
15 oz × 28.35 = 425.25 g ÷ 1000 = 0.425 kg (round at the end)
5. Forgetting Stone Includes Pounds
❌ Wrong:
"11 stone 8" to lbs: 11 × 14 = 154 lbs (forgot the 8 pounds!)
✓ Correct:
"11 stone 8" = (11 × 14) + 8 = 154 + 8 = 162 lbs
6. Assuming 1 lb = 0.5 kg
A common mental shortcut is thinking "1 lb is about half a kilogram." While this is close (1 lb = 0.454 kg), it creates 10% error:
- 100 lbs using 0.5 = 50 kg (wrong, actual is 45.4 kg)
- Better rule: "1 kg is about 2 pounds" (1 kg = 2.2 lbs, only 9% error)
7. Mixing Up Body Weight and Food Weight Scales
Different scales have different units and precision:
- Body scale: Measures in 0.1-0.5 lb or 0.1 kg increments, up to 300-400 lbs
- Kitchen scale: Measures in 1g or 0.1 oz increments, up to 5-10 lbs
- Postal scale: Measures in 0.1 oz or 1g increments, up to 50-100 lbs
Using the wrong scale can give inaccurate measurements outside its designed range.
Pro Tip:
Before any conversion, ask yourself: "Will the number get bigger or smaller?" This simple check catches most conversion errors. Going from lbs to kg? Number gets smaller. Going from kg to lbs? Number gets bigger.
Quick Reference Tables
Use these tables for fast lookups of common weight conversions:
Pounds to Kilograms
| Pounds (lbs) | Kilograms (kg) |
|---|---|
| 1 | 0.45 |
| 5 | 2.27 |
| 10 | 4.54 |
| 25 | 11.34 |
| 50 | 22.68 |
| 100 | 45.36 |
| 150 | 68.04 |
| 200 | 90.72 |
Ounces to Grams
| Ounces (oz) | Grams (g) |
|---|---|
| 1 | 28.35 |
| 2 | 56.7 |
| 4 | 113.4 |
| 8 | 226.8 |
| 12 | 340.2 |
| 16 (1 lb) | 453.6 |
Stones to Pounds and Kilograms
| Stones | Pounds | Kilograms |
|---|---|---|
| 8 | 112 | 50.8 |
| 10 | 140 | 63.5 |
| 12 | 168 | 76.2 |
| 14 | 196 | 88.9 |
| 16 | 224 | 101.6 |
Common Cooking Measurements
| Item | Ounces | Grams |
|---|---|---|
| 1 stick butter | 4 oz | 113 g |
| 1 cup flour | 4.5 oz | 125 g |
| 1 cup sugar | 7 oz | 200 g |
| 1 cup brown sugar | 7.5 oz | 220 g |
| 1 cup rice | 6.5 oz | 185 g |
Need More Conversions?
For comprehensive reference tables, check our Pounds to Kilograms Chart.
Or use our Weight Converter for instant conversions between all weight units.
Frequently Asked Questions
How many pounds are in a kilogram?
One kilogram equals approximately 2.20462 pounds. For quick mental calculations, you can use 2.2 as the conversion factor. So 1 kg ≈ 2.2 lbs. To convert kilograms to pounds, multiply by 2.2. To convert pounds to kilograms, divide by 2.2 (or multiply by 0.4536).
What is the difference between weight and mass?
Mass is the amount of matter in an object and never changes, measured in kilograms or grams. Weight is the force of gravity on that mass and varies depending on gravitational pull, technically measured in newtons. However, in everyday usage, we often use "weight" and "mass" interchangeably, and pounds/kilograms measure mass. On the Moon, your mass stays the same but your weight would be about 1/6th of Earth's.
Why does the UK use stones for weight?
The stone is a traditional British unit equal to 14 pounds (6.35 kg), historically used for weighing people and large goods. It's still commonly used in the UK and Ireland for body weight, though most other countries use kilograms. For example, someone might weigh "10 stone 5" meaning 10 stones and 5 pounds (145 lbs or 65.8 kg). The stone unit dates back to ancient times when standardized stones were used for weighing.
What is the difference between ounces and fluid ounces?
Ounces (oz) measure weight/mass - part of the imperial weight system (16 oz = 1 lb). Fluid ounces (fl oz) measure volume - part of the liquid measurement system. They're completely different: 1 oz of weight is always 1 oz, but 1 fl oz of liquid can weigh different amounts depending on the liquid's density. For example, 1 fl oz of water weighs about 1 oz, but 1 fl oz of honey weighs more.
How do you convert between metric tons and US tons?
There are three types of tons: Metric ton (tonne) = 1,000 kg = 2,204.6 lbs; US ton (short ton) = 2,000 lbs = 907.2 kg; UK ton (long ton) = 2,240 lbs = 1,016 kg. To convert: 1 metric ton = 1.102 US tons = 0.984 UK tons. The metric ton is used worldwide in most countries, while the US ton is primarily used in the United States.
What weight unit is used for body weight in different countries?
Most countries worldwide use kilograms (kg) for body weight, including all of Europe, Asia, Africa, South America, and Australia. The United States primarily uses pounds (lbs). The UK and Ireland uniquely use stones and pounds (e.g., "10 stone 5"). Medical professionals globally typically use kilograms as the standard unit regardless of country.
How accurate do I need to be with weight conversions?
Accuracy needs depend on context: Cooking/recipes: Round to the nearest 5-10 grams or 0.25 oz is usually fine; Body weight: Nearest 0.1 kg or 0.5 lb is typical; Shipping: Follow carrier requirements, usually nearest 0.1 kg or oz; Science/pharmacy: Use full precision (at least 2 decimal places); Everyday estimates: 1 kg ≈ 2.2 lbs is sufficient. For precise measurements, always use the full conversion factors.
Can I convert between grams and pounds directly?
Yes! 1 pound = 453.592 grams, and 1 gram = 0.00220462 pounds. For practical conversions: to go from grams to pounds, divide by 454 (or multiply by 0.0022); to go from pounds to grams, multiply by 454. For example, 500 grams ≈ 1.1 lbs, and 2 lbs ≈ 908 grams. For more precision, use 453.6 as the conversion factor.
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