Metric Weight Units Explained: Mg, G, Kg and Tonne
The metric system has one quiet superpower: every unit is a clean multiple of ten. Once you understand how the prefixes work, every weight from a vitamin pill to a cargo ship sits on the same simple ladder. This guide walks through that ladder one rung at a time.
What "metric" actually means
The metric system is a decimal system of measurement built around a small set of base units and standardised prefixes. For weight (more precisely, mass), the base unit is the kilogram. Every other metric weight unit is just the kilogram or the gram dressed up with a prefix that multiplies or divides it by a power of ten.
That single rule replaces the messy mix of conversion factors found in older imperial units. There is no "16 of these in one of those" or "14 pounds in a stone" — just multiplication and division by 10, 100, 1000 and so on.
When you do need those older units, keep the non-metric steps separate: pounds to stone and stone to pounds use a different rule from the metric ladder.
The metric weight ladder at a glance
Here are the metric units of weight you are most likely to meet, from the very small to the very large.
| Unit | Symbol | In grams | Common use |
|---|---|---|---|
| Microgram | µg | 0.000001 g | Vitamins, hormones, nutrients on labels |
| Milligram | mg | 0.001 g | Medicine doses, fine chemistry |
| Centigram | cg | 0.01 g | Rare in everyday use |
| Decigram | dg | 0.1 g | Rare in everyday use |
| Gram | g | 1 g | Cooking, postage, small parcels |
| Decagram | dag | 10 g | European butcher counters |
| Hectogram | hg | 100 g | Some European food labels |
| Kilogram | kg | 1,000 g | Body weight, groceries, luggage |
| Tonne | t | 1,000,000 g | Vehicles, freight, industry |
In practice, four of these do almost all the work in daily life: milligram, gram, kilogram and tonne. The others either belong to specialist fields or have fallen out of common use even in metric countries.
How metric prefixes work
A metric prefix is a small word added to the front of a base unit that tells you how many times bigger or smaller it is. The same prefixes apply to length, volume, energy and many other quantities — not just weight — which is part of why the system is so easy to learn once.
| Prefix | Symbol | Multiplier | Power of ten |
|---|---|---|---|
| micro- | µ | 0.000001 | 10⁻⁶ |
| milli- | m | 0.001 | 10⁻³ |
| centi- | c | 0.01 | 10⁻² |
| deci- | d | 0.1 | 10⁻¹ |
| (base) | — | 1 | 10⁰ |
| deca- | da | 10 | 10¹ |
| hecto- | h | 100 | 10² |
| kilo- | k | 1,000 | 10³ |
| mega- | M | 1,000,000 | 10⁶ |
So a kilogram is "one thousand grams", a milligram is "one thousandth of a gram", and a megagram (rarely used by name, but equivalent to a tonne) is "one million grams". Each step on the ladder is a factor of ten.
The four units that matter most
Milligram (mg)
One thousandth of a gram. This is the unit of medicine and small chemistry. A standard paracetamol tablet contains 500 mg of active ingredient. A grain of table salt weighs around 60 mg. You will also find milligrams on supplement labels, on cosmetic ingredient lists and in scientific work where small quantities matter.
Gram (g)
The base unit for everyday weighing. A paperclip is roughly 1 g. A US dollar bill weighs almost exactly 1 g. A standard chocolate bar is around 100 g. Recipes outside the United States are typically written in grams, and food labels list nutritional information per 100 g for easy comparison.
Grams also sit close to specialist units. Jewellers describe diamond and gemstone weight in carats, so carats to grams and grams to carats are useful whenever a certificate or product page gives both systems.
Kilogram (kg)
One thousand grams. The kilogram is the metric system's base unit of mass — every other weight unit in the system is technically defined in relation to it. In day-to-day life, the kilogram is the unit of body weight, groceries, luggage allowances and parcel shipping. A bag of sugar typically weighs 1 kg. A 2-litre bottle of water weighs about 2 kg.
Tonne (t)
One thousand kilograms, or one million grams. Also called a metric tonne to distinguish it from older imperial "tons", the tonne is the unit of vehicles, freight containers, building materials and industrial-scale shipping. A small car weighs around 1.5 t. A loaded shipping container can weigh 25–30 t.
Converting between metric weight units
Because every step on the ladder is a factor of ten, conversion is just a matter of moving the decimal point. There are no awkward multipliers like 14 or 28.35 to remember.
Each step is a multiplication or division by 1,000. To go up one rung, divide; to go down one rung, multiply.
Reference table for everyday metric conversions
The values below cover most situations where two metric weight units sit on the same label or recipe.
| From | Milligrams | Grams | Kilograms | Tonnes |
|---|---|---|---|---|
| 1 mg | 1 mg | 0.001 g | 0.000001 kg | — |
| 500 mg | 500 mg | 0.5 g | 0.0005 kg | — |
| 1 g | 1,000 mg | 1 g | 0.001 kg | — |
| 100 g | 100,000 mg | 100 g | 0.1 kg | — |
| 500 g | 500,000 mg | 500 g | 0.5 kg | 0.0005 t |
| 1 kg | 1,000,000 mg | 1,000 g | 1 kg | 0.001 t |
| 10 kg | — | 10,000 g | 10 kg | 0.01 t |
| 100 kg | — | 100,000 g | 100 kg | 0.1 t |
| 1 t | — | 1,000,000 g | 1,000 kg | 1 t |
Where each unit shows up in real life
Milligrams on a medicine label
Pharmacy labels list active ingredients in milligrams because most drug doses are tiny. A paracetamol tablet might be 500 mg, an ibuprofen tablet 200 mg, a strong painkiller 5 mg. The unit is always small and the numbers are usually round.
This page describes how the unit works. It does not give medical or dosage advice — always follow the instructions on the packaging or guidance from a qualified professional.
Grams in the kitchen
Outside the United States, almost every modern recipe is written in grams. A few useful kitchen anchors: 1 large egg is about 50 g without the shell, 1 stick of butter (US) is 113 g, 1 metric cup of plain flour is approximately 125 g.
Kilograms on the bathroom scale and the airline counter
Personal weight in metric countries is given in kilograms. Standard checked-bag limits range from 20 to 23 kg on most international airlines. This page only converts the units; it does not provide health or fitness advice. For body weight numbers in imperial form, see our kg, pounds and ounces guide.
Tonnes in industry and shipping
Once a weight gets above about a thousand kilograms, the tonne takes over. Vehicle weight ratings, freight quotations and building materials are all priced and described in tonnes. A small family car typically weighs around 1.3–1.6 t; a loaded HGV can exceed 40 t.
Where metric meets imperial
Even in fully metric countries, you sometimes need to translate between metric and imperial — old recipes, US packaging, or sports records often pull you across the divide.
| Metric | Imperial equivalent | Note |
|---|---|---|
| 1 g | 0.0353 oz | Useful for cooking |
| 100 g | 3.53 oz | About a chocolate bar |
| 1 kg | 2.20462 lb | Standard kg-to-lb factor |
| 10 kg | 22.05 lb | Cabin-bag scale |
| 1 t | 2,204.62 lb | Approx. 1.1 US short tons |
Note: a metric tonne (1,000 kg) is not the same as a US "short ton" (907.18 kg) or a UK "long ton" (1,016.05 kg). When you see "ton" without a clear context, check which one is meant before doing any maths.
For recipe and package weights, the most common pairs are grams to ounces and ounces to grams, followed by grams to pounds and pounds to grams when the quantity is larger.
For body weight, luggage and gym plates, use kilograms to pounds, pounds to kilograms, kilograms to ounces, or ounces to kilograms. Smaller imperial steps such as ounces to pounds and pounds to ounces are useful when a recipe or shipping label mixes both.
UK sources sometimes use stone for body weight. Convert kilograms to stone or stone to kilograms directly instead of rounding through pounds.
Common metric weight mistakes
- Confusing mg and g. A 500 mg tablet is half a gram, not 500 grams. The thousand-fold difference matters in pharmacy and chemistry.
- Reading "k" as "thousand pounds". The "k" in kg means "kilo-", which is "thousand grams". A kilogram is not a thousand pounds.
- Mixing tonnes and tons. Always confirm whether a source means a metric tonne or one of the imperial tons. The difference is roughly 10 percent.
- Using the wrong symbol. Kilogram is "kg", not "Kg" or "KG". Metric symbols are case-sensitive — capital "K" actually stands for the kelvin (a unit of temperature), so getting it wrong can confuse a scientific reader.
- Treating microgram and milligram as the same. A microgram (µg) is one thousandth of a milligram. The difference shows up most often in vitamin labels — vitamin D in micrograms, vitamin C in milligrams.
Why the metric system is a decimal system
The metric system was developed during the French Revolution as a deliberate replacement for the patchwork of regional units that had grown up across Europe over centuries. The goal was a universal system based on natural constants and clean decimal arithmetic — anything else, the founders argued, was just historical accident dressed up as tradition.
Its modern descendant, the International System of Units (SI), is now the official measurement system of every country in the world apart from the United States, Liberia and Myanmar. Even in those three places, science, medicine and international trade run on metric units. The kilogram itself was redefined in 2019 in terms of fundamental physical constants, completing a long-running effort to anchor every metric unit to the laws of physics rather than to a physical artefact.
Related converters and reading
If you need a single number quickly, jump straight to the converter you need:
For wider context, you may also like our complete weight conversion chart, the grams, ounces and pounds guide, and the large weight conversion guide for industrial figures.