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Weight Conversion Overview
The Weight Conversion tool converts values between metric mass units, avoirdupois units, troy units, and selected commercial mass units. Enter a value in any supported unit to calculate its equivalent in kilograms, grams, pounds, ounces, stones, tons, troy ounces, and other units.
In everyday language, weight is often used to mean mass. Strictly speaking, mass describes the amount of matter in an object, while weight is the force produced by gravity acting on that mass. This converter performs mass-unit conversions. It does not convert mass directly into force unless gravitational acceleration is also specified.
How to Use the Weight Converter
Find the input field for the unit you already know.
Enter the mass value.
Confirm whether ounce or pound means avoirdupois or troy measure.
Read the equivalent results in the other units.
Retain extra digits during calculation and round only the final value.
For trade, laboratory, medical, or precious-metal measurements, use the unit system specified by the applicable standard.
General Mass Conversion Formula
Each unit can be expressed as a factor of kilograms. To convert from one unit to another:
Target value = Source value × Source factor in kg / Target factor in kg
If the source unit is pounds and the target is kilograms, use the exact international pound definition:
10 lb × 0.45359237 kg/lb = 4.5359237 kg
To convert the result back to pounds, divide by 0.45359237:
4.5359237 kg / 0.45359237 kg/lb = 10 lb
Mass vs. Weight
| Quantity | Meaning | SI Unit |
|---|---|---|
| Mass | An object's inertial property or amount of matter. | Kilogram, kg |
| Weight | The force exerted on an object by gravity. | Newton, N |
Weight force is calculated using:
W = m × g
Here W is force in newtons, m is mass in kilograms, and g is gravitational acceleration in meters per second squared. Using standard gravity, gn = 9.80665 m/s2, a mass of 1 kg corresponds to a weight force of 9.80665 N. Actual local gravity varies with location.
SI and Metric Mass Units
The kilogram, symbol kg, is the SI base unit of mass. Metric prefixes create larger and smaller units in powers of ten.
| Unit | Symbol | Equivalent in Kilograms | Equivalent in Grams |
|---|---|---|---|
| Metric tonne | t | 1000 kg | 1000000 g |
| Kilogram | kg | 1 kg | 1000 g |
| Hectogram | hg | 0.1 kg | 100 g |
| Dekagram | dag | 0.01 kg | 10 g |
| Gram | g | 0.001 kg | 1 g |
| Decigram | dg | 0.0001 kg | 0.1 g |
| Centigram | cg | 0.00001 kg | 0.01 g |
| Milligram | mg | 0.000001 kg | 0.001 g |
| Microgram | µg | 0.000000001 kg | 0.000001 g |
| Nanogram | ng | 0.000000000001 kg | 0.000000001 g |
| Picogram | pg | 0.000000000000001 kg | 0.000000000001 g |
SI symbols are case-sensitive. The correct symbol for kilogram is kg, not Kg, and the symbol for milligram is mg, not MG.
Avoirdupois Mass Units
The avoirdupois system is used for most everyday goods in the United States and for common pound and ounce measurements. One avoirdupois pound contains 16 avoirdupois ounces or 7000 grains.
| Unit | Symbol | Equivalent Mass |
|---|---|---|
| Short ton | short ton | 2000 lb = 907.18474 kg |
| Short hundredweight | cwt | 100 lb = 45.359237 kg |
| Stone | st | 14 lb = 6.35029318 kg |
| Pound | lb | 0.45359237 kg |
| Avoirdupois ounce | oz | 28.349523125 g |
| Avoirdupois dram | dr | 1.7718451953125 g |
| Grain | gr | 64.79891 mg |
Long Ton and Imperial Avoirdupois Units
| Unit | Pounds | Kilograms |
|---|---|---|
| Long hundredweight | 112 lb | 50.80234544 kg |
| Long ton | 2240 lb | 1016.0469088 kg |
The words ton and hundredweight are ambiguous unless the system is stated. A metric tonne, U.S. short ton, and Imperial long ton are three different masses.
Troy Mass Units
Troy units are commonly used for precious metals. A troy ounce is heavier than an avoirdupois ounce, but a troy pound is lighter than an avoirdupois pound because the troy pound contains only 12 troy ounces.
| Troy Unit | Symbol | Equivalent Mass |
|---|---|---|
| Troy pound | lb t | 12 oz t = 373.2417216 g |
| Troy ounce | oz t | 480 gr = 31.1034768 g |
| Pennyweight | dwt | 24 gr = 1.55517384 g |
| Grain | gr | 64.79891 mg |
The grain has the same mass in the avoirdupois, troy, and apothecaries systems. The systems differ in how many grains make an ounce or pound.
Avoirdupois Ounce vs. Troy Ounce
| Unit | Grains | Grams | Typical Use |
|---|---|---|---|
| Avoirdupois ounce | 437.5 gr | 28.349523125 g | Everyday goods and general commerce |
| Troy ounce | 480 gr | 31.1034768 g | Precious metals |
One troy ounce is approximately 9.7% heavier than one avoirdupois ounce. Always include the word troy or the symbol oz t when the distinction matters.
Carat and Other Specialized Units
| Unit | Symbol | Equivalent Mass | Typical Use |
|---|---|---|---|
| Metric carat | ct | 200 mg = 0.2 g | Gemstone mass |
| Grain | gr | 64.79891 mg | Small masses and selected industries |
| Pennyweight | dwt | 1.55517384 g | Precious metals and jewelry |
Do not confuse carat, a unit of gemstone mass, with karat, a measure of gold purity.
Units and Conversion Values
The original page included the following mass-unit reference image. It has been retained for comparison with the calculator fields.
Worked Conversion Examples
Pounds to Kilograms
Convert 150 lb to kilograms:
150 × 0.45359237 = 68.0388555 kg
Kilograms to Pounds
Convert 2.5 kg to pounds:
2.5 / 0.45359237 = 5.51156 lb
Troy Ounces to Grams
Convert 10 troy ounces to grams:
10 × 31.1034768 = 311.034768 g
Stone to Kilograms
Convert 5 stone to kilograms:
5 × 6.35029318 = 31.7514659 kg
Grams to Avoirdupois Ounces
Convert 750 g to ounces:
750 / 28.349523125 = 26.4555 oz
Tonne, Short Ton, and Long Ton Comparison
| Unit | Kilograms | Pounds |
|---|---|---|
| Metric tonne | 1000 kg | 2204.62262 lb |
| U.S. short ton | 907.18474 kg | 2000 lb |
| Imperial long ton | 1016.0469088 kg | 2240 lb |
Write tonne, short ton, or long ton rather than ton alone when the context could be international.
Significant Digits and Measurement Uncertainty
An exact conversion factor does not make the original measurement exact. A value measured as 10 lb should not automatically be reported with many decimal places simply because the calculator can display them. Keep sufficient digits during the calculation, then round the final value to match the measurement uncertainty and purpose.
Commercial scales, laboratory balances, kitchen scales, and industrial weighing systems have different readability, capacity, calibration, and uncertainty. The converter changes units; it does not improve the accuracy of the original measurement.
Common Weight Conversion Mistakes
Using liters or cubic meters in a mass conversion without knowing density.
Confusing an avoirdupois ounce with a troy ounce.
Confusing a short ton, metric tonne, and long ton.
Treating kilogram-force as the same quantity as kilogram mass.
Using lb when lbf, a unit of force, is intended.
Confusing carat mass with karat gold purity.
Using fluid ounces, which measure volume, in a mass conversion.
Ignoring the density required to convert between volume and mass.
Rounding intermediate values before completing the calculation.
Reporting more significant digits than the original measurement supports.
Converting Volume to Mass
Volume cannot be converted directly to mass unless the material density is known. The relationship is:
Mass = Density × Volume
Density may change with temperature, pressure, composition, and concentration. This is why one cup of water and one cup of oil do not necessarily have the same mass, even though their volumes are equal.
Frequently Asked Questions
What is the SI unit of mass?
The kilogram, symbol kg, is the SI base unit of mass.
What is the difference between mass and weight?
Mass is an intrinsic property measured in kilograms. Weight is a force caused by gravity and is measured in newtons.
How many kilograms are in one pound?
One international avoirdupois pound equals exactly 0.45359237 kg.
How many grams are in one ounce?
One avoirdupois ounce equals 28.349523125 g. One troy ounce equals 31.1034768 g, so the unit system must be specified.
How many pounds are in one stone?
One stone equals 14 avoirdupois pounds.
Is a metric tonne the same as a U.S. ton?
No. A metric tonne is 1000 kg, while a U.S. short ton is 907.18474 kg.
Is a troy pound heavier than a standard pound?
No. A troy pound is 373.2417216 g, while an avoirdupois pound is 453.59237 g. The troy ounce is heavier, but the troy pound contains only 12 troy ounces.
Can kilograms be converted directly to newtons?
Only after selecting gravitational acceleration. Under standard gravity, multiply kilograms by 9.80665 to obtain weight force in newtons.
Can milliliters be converted directly to grams?
Not without density. For water near ordinary conditions the numerical values may be similar, but that shortcut does not apply to all materials or precision work.
