Weight & Mass Unit Conversion: Kilograms, Pounds, Stone, Ounces & More
Weight and mass conversions are among the most common arithmetic tasks people face daily — whether you are reading a recipe, checking shipping limits, following a fitness plan, or interpreting a scientific result. Understanding the relationships between kilograms, pounds, ounces, stone, grams, and metric tons prevents costly errors and removes the mental friction of switching between measurement systems.
The Metric and Imperial Weight Systems
The International System of Units (SI) uses the kilogram (kg) as its base unit of mass. The imperial/US customary system centres on pounds (lb) and ounces (oz). The UK also uses the stone (st), equal to 14 pounds, primarily for personal body weight. Knowing which system a document uses is the first step to avoiding conversion mistakes.
Exact Conversion Factors
| From | To | Multiply by |
|---|---|---|
| Kilograms (kg) | Pounds (lb) | 2.20462262 |
| Pounds (lb) | Kilograms (kg) | 0.45359237 |
| Grams (g) | Ounces (oz) | 0.03527396 |
| Ounces (oz) | Grams (g) | 28.34952313 |
| Kilograms (kg) | Stone (st) | 0.15747304 |
| Stone (st) | Kilograms (kg) | 6.35029318 |
| Grams (g) | Pounds (lb) | 0.00220462 |
| Pounds (lb) | Grams (g) | 453.59237 |
| Metric tons (t) | Kilograms (kg) | 1000 |
| Kilograms (kg) | Metric tons (t) | 0.001 |
Worked Examples
Example 1 — Kilograms to Pounds: A gym bag weighs 12 kg. To convert: 12 × 2.20462 ≈ 26.46 lb. Verify instantly with the Kilograms to Pounds converter.
Example 2 — Pounds to Stone and Pounds: A person weighs 168 lb. Divide by 14: 168 ÷ 14 = 12 stone exactly. Use the Pounds to Kilograms converter to also get the metric equivalent (76.2 kg), then cross-check with the Kilograms to Stone converter.
Example 3 — Grams to Ounces (cooking): A recipe calls for 250 g of flour. 250 × 0.035274 ≈ 8.82 oz. The Grams to Ounces converter handles this in one click.
Example 4 — Metric Tons to Kilograms (freight): A shipment is listed as 3.75 metric tons. 3.75 × 1000 = 3,750 kg. The Metric Tons to Kilograms converter is useful for logistics and materials science.
Understanding Stone: A UK-Specific Unit
The stone is rarely used outside the United Kingdom and Ireland, yet it persists firmly in British culture for describing human body weight. One stone equals exactly 14 pounds or approximately 6.35029 kg. When a UK doctor notes a patient's weight as "11 st 4 lb", that equals 158 lb or 71.67 kg. The Stone to Kilograms converter handles combined stone-and-pounds entries correctly.
Mass vs Weight: A Brief Note
Strictly speaking, mass is the amount of matter in an object (measured in kg), while weight is the gravitational force acting on that mass (measured in Newtons). In everyday life the terms are used interchangeably because we live on the surface of a single planet where gravitational acceleration is nearly constant (9.80665 m/s²). All the converters on this site deal with mass, which is what bathroom scales, postal services, and kitchen recipes all refer to.
Common Mistakes to Avoid
- Confusing grams and ounces in recipes. US recipes use volume for dry ingredients but weight for precision baking, often in ounces. UK/European recipes use grams. Always check which system the recipe is written in before converting. Use the Ounces to Grams or Grams to Pounds converters to switch systems.
- Mixing troy and avoirdupois ounces. A troy ounce (used for precious metals) equals 31.1035 g, while a standard (avoirdupois) ounce equals 28.3495 g — a 10% difference. Precious metals are always traded in troy ounces.
- Rounding too early. When chaining conversions (lb → kg → stone), retain full precision until the final step to prevent accumulated rounding errors.
- Assuming metric tons and US tons are the same. A metric ton is 1,000 kg; a US (short) ton is 2,000 lb (≈907.185 kg). They differ by about 10%.
Frequently Asked Questions
How many pounds are in a kilogram?
Exactly 2.20462262 pounds. For a quick mental estimate, multiply kilograms by 2.2.
What is 70 kg in stone and pounds?
70 kg ÷ 6.35029 ≈ 11.023 stone, which is 11 stone 0.32 lb — commonly rounded to 11 st 0 lb.
Why does the UK use stone for body weight?
The stone is a historic English unit that became culturally entrenched for describing human weight. Despite metrication in many areas, it remains in widespread informal use in the UK and Ireland.
Is a kilogram heavier than a pound?
Yes. One kilogram equals approximately 2.205 pounds, so a kilogram is more than twice as heavy as a pound.