Weight Converter.
Convert between metric, imperial, troy, and scientific weight units instantly. Covers kilograms, pounds, ounces, grams, stones, metric tons, carats, and more.
Precision
How many significant digits to display in results.
Number Format
Always show exponential form (e.g. 1.602e−19). Enabled automatically for very large or very small values such as atomic mass units.
Unit Reference
Metric — Base: gram (g). 1 kg = 1 000 g · 1 t = 1 000 kg · 1 q = 100 kg.
Imperial — 1 lb = 453.592 g · 1 oz = 28.3495 g · 1 st = 14 lb · 1 sh tn = 2 000 lb.
Troy — Used for precious metals. 1 oz t = 31.1035 g · 1 lb t = 12 oz t.
Scientific — 1 ct = 0.2 g (gemstones) · 1 u ≈ 1.661 × 10⁻²⁴ g (atomic mass).
Unit Reference
Metric System (SI)
The SI base unit of mass is the kilogram (kg), defined since 2019 by fixing Planck's constant to exactly 6.626 070 15 × 10⁻³⁴ J·s. All metric weights are powers of ten: 1 kg = 1 000 g, 1 t = 1 000 kg, 1 mg = 0.001 g. The gram is used as the conversion base in this tool.
Imperial & US Customary
The international pound was standardised in 1959 to exactly 453.592 37 g, fixing all derived units: 1 oz = 1/16 lb = 28.349 5 g, 1 stone = 14 lb, 1 short ton = 2 000 lb. The UK long ton equals 2 240 lb (1 016.047 kg). Imperial units are common in the USA, UK, and some Commonwealth countries.
Troy System
Troy weights are used globally for precious metals — gold, silver, and platinum are always quoted in troy ounces. One troy ounce = 31.103 5 g, about 10% heavier than an avoirdupois ounce. A troy pound has only 12 troy ounces (373.24 g), lighter than the 16-oz avoirdupois pound. Pennyweight (dwt) = 1/20 troy oz.
Scientific Units
The carat (ct) is the standard mass unit for gemstones: 1 ct = 0.2 g exactly (adopted internationally in 1907). The atomic mass unit (u or Da) equals 1/12 the mass of a carbon-12 atom: ≈ 1.6605 × 10⁻²⁴ g. It is fundamental in chemistry and physics for expressing molecular and atomic masses.
How weight conversion works
All conversions go through a common base — the gram. Multiplying by the source unit's grams-per-unit factor converts to grams; dividing by the target unit's factor converts from grams to the result. For example, 5 pounds to kilograms: 5 × 453.592 37 ÷ 1 000 = 2.268 kg.
Kilograms to pounds
1 pound = 453.592 37 g exactly, so 1 kg = 1 000 ÷ 453.592 37 ≈ 2.2046 lb. To convert kg to lbs, multiply by 2.2046. A person weighing 70 kg ≈ 154.32 lb. This is the most common conversion for body weight outside the USA.
Grams to ounces
1 ounce (avoirdupois) = 28.349 523 125 g exactly. To convert g → oz, divide by 28.3495. Common reference: 100 g ≈ 3.527 oz. Cooking recipes from the USA often list ingredients in ounces, while European recipes use grams.
Stone to kilograms
One stone = 14 pounds = 6.350 29 kg. Body weight in the UK is traditionally expressed in stones and pounds. A person weighing 11 stone = 154 lb ≈ 69.85 kg.
Troy ounce vs avoirdupois ounce
A troy ounce (31.103 5 g) is heavier than a regular avoirdupois ounce (28.349 5 g) by about 9.7%. Gold prices are always quoted per troy ounce. Do not confuse the two when weighing precious metals — using the wrong ounce introduces a ~10% error.
Carats for gemstones
The metric carat (ct) equals exactly 0.2 g. A 1-carat diamond weighs 200 mg. Note that "carat" for gemstones (mass) is different from "karat" for gold purity (fineness). Large gemstones are described in carats; the Hope Diamond is 45.52 ct ≈ 9.1 g.
Frequently Asked Questions
- How do I convert kilograms to pounds?
- Multiply kilograms by 2.20462 to get pounds (1 kg = 2.20462 lb exactly). For the reverse, divide pounds by 2.20462. Quick check: 70 kg ≈ 154.3 lb.
- How many grams are in an ounce?
- One avoirdupois ounce equals exactly 28.349523125 grams. To convert grams to ounces, divide by 28.3495. Note: a troy ounce (used for precious metals) is 31.1035 g — about 10% heavier than a regular ounce.
- What is the difference between a troy ounce and a regular ounce?
- An avoirdupois ounce (everyday use) = 28.3495 g. A troy ounce (gold, silver, platinum) = 31.1035 g — about 9.7% heavier. Gold prices and all precious metal weights are always quoted in troy ounces.
- How many pounds are in a stone?
- One stone equals exactly 14 pounds (6.35029 kg). Body weight in the UK is traditionally expressed in stones and pounds. For example, 11 stone 4 lb = 158 lb ≈ 71.7 kg.
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