Metric Mass Converter
Convert milligrams, grams, kilograms, metric tonnes and every current SI-prefixed gram unit. Choose any source and target unit, set decimal-place or significant-figure precision, and review the exact value, power-of-ten factor and calculation steps.
- 26 metric mass entries
- Exact rational arithmetic
- All 24 current SI prefixes
- Decimal or significant-figure rounding
Convert Metric Mass Units
Enter a nonnegative decimal, scientific-notation value, simple fraction or mixed number. Every unit factor is an exact power of ten. The selected precision changes only the displayed result.
1000 mg converted by exact SI powers of ten.
Common Metric Equivalents
| Unit | Equivalent mass |
|---|---|
| metric tonne (t) | 0.000001 t |
| megagram (Mg) | 0.000001 Mg |
| kilogram (kg) | 0.001 kg |
| gram (g) | 1 g |
| milligram (mg) | 1000 mg |
| microgram (µg) | 1000000 µg |
| nanogram (ng) | 1000000000 ng |
Calculation Steps
- Express the source unit as 1 mg = 10^-3 g.
- Express the target unit as 1 g = 10^0 g.
- Multiply 1000 by 10^(-3 - 0) to obtain exactly 1 g.
- Apply the selected six-place display only after conversion.
The prefix factor is exact. The six decimal places format the answer but do not add accuracy to the original measurement.
The browser blocked automatic copying. The complete result is selected. Press Ctrl+C on Windows or Command+C on macOS.
How to Use This Metric Mass Converter
Allow about two minutes for one conversion, including a quick check of the unit symbols and reporting precision.
- Enter one mass. Use a decimal such as 0.125, scientific notation such as 3.6e-7, a fraction such as 1/2, or a mixed number such as 1 1/2. Leave the unit symbol out.
- Select the source unit. Choose the unit attached to your entered value and check capitalization, especially mg versus Mg.
- Select the target unit. Choose any common metric unit or current SI-prefixed gram unit.
- Choose display precision. Select decimal places or significant figures, enter the required count, and choose a tie rule.
- Press Convert. Review the displayed result, exact target, power-of-ten factor, common equivalents and calculation steps.
- Copy, swap or reset. Copy the complete result, swap units with the exact internal value, or restore the 1000 mg to 1 g example.
Zero is valid. A negative entry is rejected because this page converts a physical mass, not a signed change. Fractions remain exact rational values. The calculator keeps the unrounded result when you swap units, even when the displayed decimal was shortened.
Metric Mass Conversion Formula
Every supported prefixed gram unit has an exact decimal exponent relative to one gram. Milligram is 10−3 g, kilogram is 103 g, and quettagram is 1030 g. To convert, subtract the target exponent from the source exponent and multiply by the resulting power of ten.
For kilograms to milligrams, the source exponent is 3 and the target exponent is −3. Their difference is 6, so multiply by 106. For milligrams to kilograms, the difference is −6, so multiply by 10−6. The operation moves the decimal point, but the exact rational engine also handles fractions and extreme exponents without converting them to binary floating point.
Why gram is the calculation basis
The kilogram is the SI base unit of mass, but SI names and symbols for its decimal multiples and submultiples attach prefixes to gram. The standard forms are milligram and megagram, not microkilogram or kilokilogram. Using gram exponents gives one consistent conversion rule across the complete prefix range.
Worked Metric Mass Examples
Example 1: Convert 1000 mg to g
Milligram has exponent −3 and gram has exponent 0. Multiply 1000 by 10−3. The exact result is 1 g.
Example 2: Convert 2.5 kg to mg
Kilogram has exponent 3 and milligram has exponent −3. The difference is 6. Multiply 2.5 by 106 to obtain exactly 2,500,000 mg.
Example 3: Convert 750 mg to g
Multiply 750 by 10−3. The exact result is 0.75 g. Writing 0.750 g may communicate a chosen display precision, but it does not prove how accurately the original mass was measured.
Example 4: Convert 3 tonnes to kilograms
One tonne equals exactly 1000 kg, so 3 t equals exactly 3000 kg. Tonne and megagram have the same mass: 1 t = 1 Mg.
Example 5: Convert 1 Qg to qg
Quettagram is 1030 g and quectogram is 10−30 g. The exponent difference is 60, so 1 Qg equals exactly 1060 qg. Capitalization changes the unit by sixty powers of ten in this extreme pair.
Metric Mass Units and Current SI Prefixes
The current SI system has 24 prefixes. Quetta, ronna, ronto and quecto were added in 2022. The table combines each prefix with gram and adds the tonne, a non-SI unit accepted for use with SI and exactly equal to one megagram.
| Unit | Symbol | Exact factor in grams |
|---|---|---|
| quettagram | Qg | 1030 g |
| ronnagram | Rg | 1027 g |
| yottagram | Yg | 1024 g |
| zettagram | Zg | 1021 g |
| exagram | Eg | 1018 g |
| petagram | Pg | 1015 g |
| teragram | Tg | 1012 g |
| gigagram | Gg | 109 g |
| megagram | Mg | 106 g |
| metric tonne | t | 106 g = 1000 kg |
| kilogram | kg | 103 g |
| hectogram | hg | 102 g |
| decagram | dag | 101 g |
| gram | g | 100 g |
| decigram | dg | 10−1 g |
| centigram | cg | 10−2 g |
| milligram | mg | 10−3 g |
| microgram | µg | 10−6 g |
| nanogram | ng | 10−9 g |
| picogram | pg | 10−12 g |
| femtogram | fg | 10−15 g |
| attogram | ag | 10−18 g |
| zeptogram | zg | 10−21 g |
| yoctogram | yg | 10−24 g |
| rontogram | rg | 10−27 g |
| quectogram | qg | 10−30 g |
Uncommon prefix combinations are mathematically valid, though science and industry usually choose a unit that keeps the numerical value easy to read. Tonne is a non-SI unit accepted for use with SI. It must not be confused with the US short ton or Imperial long ton.
Common Metric Mass Conversions
| Starting unit | Exact equivalents |
|---|---|
| 1 µg | 0.001 mg = 1000 ng |
| 1 mg | 0.001 g = 1000 µg |
| 1 g | 1000 mg = 0.001 kg |
| 1 kg | 1000 g = 1,000,000 mg |
| 1 Mg | 1000 kg = 1 t |
| 1 t | 1 Mg = 1000 kg = 1,000,000 g |
These equalities are exact unit relationships. Commas in the table improve readability, but the calculator input intentionally rejects commas so a value cannot be misread under different regional number conventions.
Kilogram, Gram, Tonne and Symbol Rules
The kilogram, symbol kg, is the SI base unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be exactly 6.62607015 × 10−34 when expressed in the unit J s. The definition does not depend on a physical kilogram artifact.
Mass is the one SI base quantity whose unit name already contains a prefix. For this historical reason, further multiples and submultiples are formed from gram. Write mg for milligram, not µkg. Compound prefixes such as mkg or kkg are not valid SI forms.
Symbols are case-sensitive. Lowercase mg means milligram, 10−3 g. Uppercase Mg means megagram, 106 g. One Mg is one billion mg. The tonne symbol is lowercase t, while T is the prefix symbol for tera.
Exact Factors, Rounding and Measurement Precision
SI prefix factors are exact powers of ten. That makes the mathematical conversion exact, but it does not make the entered measurement exact. A laboratory balance, kitchen scale, shipping scale or product label still has resolution, calibration limits and uncertainty.
Keep four ideas separate:
- Exact unit factor: the power-of-ten relationship between two metric mass units.
- Exact mathematical result: the entered decimal or fraction multiplied by that factor.
- Displayed result: the exact value rounded to the selected decimal places or significant figures.
- Measured result: a report limited by the source measurement and its intended use.
The default rule is round-to-nearest, ties-to-even. In an exact halfway case, the retained last digit becomes even. The alternate ties-away rule moves a halfway magnitude away from zero. An approximation sign appears only when the selected display differs from the exact rational target.
Metric Mass Is Not Weight or Volume
This page converts mass units. In physics, weight is a force caused by gravity. The SI unit of force is the newton. A kilogram mass has the same mass in different gravitational fields, while its weight force changes with local acceleration.
Grams also do not convert directly to millilitres with one universal factor. Grams measure mass and millilitres measure volume. A mass-to-volume calculation needs the material’s density or a valid concentration under stated conditions. The converter therefore excludes litres, millilitres, newtons, pounds-force and density assumptions.
Common Metric Mass Conversion Mistakes
- Mixing mg and Mg. Milligram and megagram differ by a factor of 109.
- Using T for tonne. The tonne symbol is t. Uppercase T is the tera prefix.
- Attaching another prefix to kilogram. Use prefixed gram names such as mg and Mg.
- Moving the decimal in the wrong direction. Subtract the target exponent from the source exponent before choosing left or right.
- Confusing tonne with other tons. One tonne is 1000 kg. US short ton and Imperial long ton are different units.
- Rounding an intermediate answer. Apply the exact power of ten first and round only the final display.
- Creating false precision. Extra digits do not improve an uncertain or coarsely measured input.
- Converting mass to volume without density. There is no universal grams-to-millilitres factor.
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Frequently Asked Questions
How do I convert between milligrams, grams and kilograms?
Use their exact gram exponents. Milligram is 10^-3 g, gram is 10^0 g and kilogram is 10^3 g. Multiply the input by 10 raised to the source exponent minus the target exponent.
How many milligrams are in one gram?
One gram equals exactly 1000 milligrams. In the reverse direction, one milligram equals exactly 0.001 gram.
How many grams are in one kilogram?
One kilogram equals exactly 1000 grams. Therefore one gram equals exactly 0.001 kilogram.
How many kilograms are in one metric tonne?
One metric tonne, symbol t, equals exactly 1000 kilograms. It also equals one megagram and one million grams.
Is one megagram the same as one tonne?
Yes. One megagram, 1 Mg, and one tonne, 1 t, both equal exactly 1000 kg or 1,000,000 g.
What is the difference between mg and Mg?
Lowercase mg means milligram, which is 10^-3 g. Uppercase Mg means megagram, which is 10^6 g. One Mg equals one billion mg.
What does the symbol µg mean?
The symbol µg means microgram. One microgram equals exactly 10^-6 g, 0.001 mg or 1000 ng.
Why do mass prefixes attach to gram instead of kilogram?
The kilogram is the SI base unit, but its name already contains a prefix for historical reasons. SI rules form decimal multiples and submultiples by attaching one prefix to gram.
Are metric mass conversions exact?
Yes. SI prefix relationships and the tonne-to-kilogram relationship are exact. The original measurement may still have uncertainty, and a selected display may round the exact mathematical result.
Does this calculator convert mass to weight or volume?
No. Weight is a force, and mass-to-volume conversion requires density or concentration. This page converts only compatible metric mass units.
Calculation Method and Review Basis
- BIPM SI Brochure, 9th edition, current SI definitions, prefix rules and tonne relationship.
- BIPM SI Prefixes, the current 24-prefix table.
- BIPM Kilogram Definition, the current constant-based SI base-unit definition.
- 27th CGPM Resolution 3, addition of quetta, ronna, ronto and quecto.
- NIST SI Units of Mass, kilogram, gram and mass-versus-weight guidance.
- NIST Metric Prefixes, prefix names, symbols and exact powers.
- NIST Handbook 44, 2026 Appendix C, current measurement tables and metric-unit notes.
Measurement disclaimer: This converter applies exact metric unit relationships to the value you enter. It does not certify a balance, scale, laboratory result, medicine dose, shipping declaration, legal-metrology result or material density. Confirm unit symbols, calibration, uncertainty, significant digits and the applicable authority before relying on a conversion for trade, health, laboratory, engineering, legal or safety work.