Weight Converter

What Is the Weight Converter?

The weight converter lets you switch over between the most commonly used units of weight and mass, from milligrams at the small end to metric tonnes at the large end, including the imperial units of ounces, pounds, and stone that remain in everyday use in the US and UK. The conversion factors follow the definitions set out by NIST and the BIPM, so results are precise and consistent with international standards.

In practice, weight conversions come up in cooking, fitness, shipping, science, and medicine. The UK in particular uses a mix of metric and imperial in everyday life: body weight is often expressed in stone and pounds, food packaging uses grams and kilograms, and postal rates are based on grams. Being able to figure out any one of these in terms of another quickly saves a lot of back-and-forth.

Common Units and When to Use Them

Technically, weight and mass are different physical quantities: mass is measured in kilograms and refers to the amount of matter, while weight is the force exerted by gravity and is measured in Newtons. In everyday usage, however, the two terms are used interchangeably, and the units below all refer to mass in the scientific sense.

• Milligram (mg): Used in medicine for drug dosages and in chemistry for very small quantities. One milligram equals 0.001 grams.
• Gram (g): The standard unit for food ingredients, nutritional information, and small quantities of material. One gram equals 0.001 kilograms.
• Kilogram (kg): The SI base unit of mass. Used for body weight in most countries, food products sold by weight, and most everyday weight measurements outside the US.
• Metric tonne (t): Used for vehicle weights, freight, industrial quantities, and large-scale commodity pricing. One metric tonne equals exactly 1,000 kilograms.
• Ounce (oz): Used in the US and UK for small food quantities, postal weights, and precious metals. One ounce equals approximately 28.3495 grams.
• Pound (lb): The primary everyday weight unit in the US. Body weight, food, and most retail products in the US are measured in pounds. One pound equals exactly 453.592 grams.
• Stone (st): Used primarily in the UK and Ireland for body weight. One stone equals exactly 14 pounds or approximately 6.350 kilograms.
• US ton (short ton): Used in the US for freight and industrial quantities. One short ton equals 2,000 pounds or approximately 907 kilograms.

How Conversion Works

All weight conversions work by expressing every unit as a fixed number of grams, then dividing by the gram equivalent of the target unit. The kilogram is the SI base unit, and all metric conversions are exact powers of ten. Imperial units are defined in terms of exact gram equivalents established by international agreement in 1959, so these conversions are also precise rather than approximate.

Practical Applications

Cooking is one of the most common reasons people look up weight conversions. American recipes typically use cups and ounces, while European recipes use grams. Converting 8 oz of flour to grams works out to 227 grams, but the actual weight will vary slightly depending on how tightly the flour is packed, which is why professional bakers prefer grams for accuracy. On top of that, ingredient densities vary, so volume-to-weight conversions for cooking require ingredient-specific tables rather than a simple unit converter.

For fitness and health, body weight is the most obvious use case. Many UK residents know their weight in stone and pounds but need kilograms for medical forms, gym equipment settings, and BMI calculations. Our BMI Calculator accepts both kg and lb, but if you are dealing with a system that only accepts one format, this converter lets you work it out instantly. As a reference point, 70 kg equals about 11 stone, 154 pounds, or 10 st 10 lb in UK notation.

In shipping and logistics, both metric and imperial weight limits come up regularly. Parcel services often specify limits in kilograms, while some US couriers use pounds. Airlines have baggage weight limits in kilograms for international flights. Being able to figure out whether a 23 kg luggage allowance is equivalent to about 50.7 lb helps when packing for a US airline that lists limits in pounds.

Pro Tips

• A rough mental conversion for kg to pounds: multiply by 2.2. For pounds to kg: multiply by 0.45 or divide by 2.2. For most everyday purposes this level of precision is fine.
• To convert stone to kilograms, multiply the stone value by 6.35. So 12 stone equals 12 x 6.35 = 76.2 kg.
• When dealing with precious metals, note that the troy ounce (31.1035 g) differs from the avoirdupois ounce (28.3495 g) used for everyday weights. This converter uses avoirdupois ounces.
• For pharmaceutical and scientific work, always use milligrams and grams rather than ounces to avoid dosage errors. The difference between an ounce and a gram is significant at small quantities.

You may also find our BMI Calculator and Length Converter useful for health and fitness calculations that involve both weight and height.

Conclusion

Weight is measured in a mix of metric and imperial units that varies by country, industry, and context, and the UK in particular uses both systems simultaneously in everyday life. This converter covers all the units you are likely to deal with, from milligrams for precise scientific or medical use to metric tonnes for industrial quantities, using exact conversion factors defined by international standards. Whether you are adapting a recipe, calculating a luggage allowance, or converting a medical weight record, it gives you an accurate answer without the arithmetic.