Metric Conversion Calculator for SI Units and Prefixes
Convert metric values across every current SI decimal prefix. Handle length, area, volume, mass, temperatures, time, speed, acceleration, force, pressure, energy, power and frequency without binary floating-point rounding.
- All 24 SI prefixes
- Square and cube rules
- Exact decimal arithmetic
- Separate temperature intervals
Online Metric Conversion Calculator
Select a quantity, enter one signed decimal or scientific-notation value, then choose the source and target units. Fahrenheit and Rankine appear only as temperature reference scales. For broader non-metric conversions, use the Unit Conversion and Measurement Calculators hub.
The displayed output exactly represents the stored conversion.
Equivalent Units
Every row starts from the same exact source value; rounded row values are labelled.
| Unit | Equivalent value |
|---|---|
| micrometres (µm) | 1e9 µm |
| millimetres (mm) | 1000000 mm |
| centimetres (cm) | 100000 cm |
| metres (m) | 1000 m |
| kilometres (km) | 1 km |
Calculation Steps
- Read the source as the exact decimal 1 km.
- Convert the source to m with its stored reference factor.
- Divide by the target-unit factor; the combined factor is 1000.
- Report 1000 m and keep the unrounded rational value for every equivalent row.
Length uses a linear prefix factor. Do not reuse this factor unchanged for square or cubic units.
How to Use the Metric Conversion Calculator
A complete conversion usually takes about two minutes.
- Choose the quantity. Select SI prefix, length, area, volume, mass, temperature, temperature interval, time, speed, acceleration, force, pressure, energy, power or frequency.
- Choose the base SI unit when needed. Universal prefix mode lets you apply prefixes to metres, grams, seconds and SI units with special names.
- Enter the source value. Use a signed decimal or scientific-notation number without commas, unit symbols or a written formula.
- Select the source and target units. Read symbols carefully: M is mega, m is milli or metre by context, k is kilo, and K is kelvin.
- Set displayed precision. Choose four to twelve significant digits. This changes only the displayed result.
- Convert or swap. Convert the value, or swap the unit selectors while preserving the exact entered text.
- Review the method. Check the base SI value, factor, equivalent-unit table, calculation steps and quantity-specific limits before using the result.
What Is a Metric Conversion?
A metric conversion changes the numerical value and unit used to express one physical quantity. The quantity itself does not change. A distance of 1 kilometre is the same distance as 1000 metres, 100,000 centimetres or 1,000,000 millimetres.
The International System of Units, called SI, organizes coherent base and derived units. Decimal prefixes form multiples and submultiples of those units. Kilo means 103, milli means 10-3, micro means 10-6, and the complete official range now extends from quetta at 1030 to quecto at 10-30.
This page stays metric-first. Fahrenheit and Rankine are included only as reference scales in the temperature modes. U.S. customary and Imperial length, area, volume and mass units remain outside this tool, which avoids ambiguous names such as gallon, ounce or ton.
Metric Quantities and Reference Units
| Mode | Reference unit | Special handling |
|---|---|---|
| Universal prefix | Selected unprefixed SI unit | All 24 prefixes from quetta to quecto |
| Length | metre (m) | Linear prefix factor |
| Area | square metre (m²) | Prefix factor is squared; hectare included |
| Volume | cubic metre (m³) | Prefix factor is cubed; litre prefixes included |
| Mass | kilogram (kg) | Prefixes attach to gram; tonne included |
| Temperature value | kelvin (K) | Exact scale and offset formulas |
| Temperature interval | kelvin interval (K) | Scale only, no zero-point offset |
| Time and motion | s, m/s or m/s² | Minutes, hours, days and km/h are labelled |
| Derived SI units | N, Pa, J, W or Hz | Every current decimal prefix |
Metric Conversion Formula
For two linear units that share one reference unit, multiply by the source factor and divide by the target factor:
For ordinary prefixed units, the same relationship becomes a power-of-ten shift. If the source prefix exponent is a and the target prefix exponent is b, a linear conversion uses 10a-b.
Area and volume require dimensional exponents. A square centimetre is not one hundredth of a square metre. The centimetre factor must be squared. A cubic centimetre uses the cube of the centimetre factor.
Temperature values are affine rather than simple prefix conversions. The calculator first converts the source value to kelvin, checks the absolute-zero boundary, then converts kelvin to the target scale. Temperature intervals use scale factors only and never use the 273.15 or 32-degree offsets.
Current SI Prefixes
Prefix symbols are case-sensitive. The tool includes the four prefixes added in 2022: quetta, ronna, ronto and quecto. It also preserves the two-character symbol da for deca and displays the correct micro sign.
| Large prefix | Factor | Small prefix | Factor |
|---|---|---|---|
| quetta (Q) | 1030 | deci (d) | 10-1 |
| ronna (R) | 1027 | centi (c) | 10-2 |
| yotta (Y) | 1024 | milli (m) | 10-3 |
| zetta (Z) | 1021 | micro (µ) | 10-6 |
| exa (E) | 1018 | nano (n) | 10-9 |
| peta (P) | 1015 | pico (p) | 10-12 |
| tera (T) | 1012 | femto (f) | 10-15 |
| giga (G) | 109 | atto (a) | 10-18 |
| mega (M) | 106 | zepto (z) | 10-21 |
| kilo (k) | 103 | yocto (y) | 10-24 |
| hecto (h) | 102 | ronto (r) | 10-27 |
| deca (da) | 101 | quecto (q) | 10-30 |
Worked Metric Conversion Examples
Example 1: kilometres to metres
Kilo represents 103. The unprefixed metre has exponent zero, so the exponent difference is 3. Multiply by 1000.
Example 2: square centimetres to square metres
Centi represents 10-2, but an area contains two length dimensions. Square the scale factor.
Example 3: cubic centimetres to millilitres
One cubic centimetre equals 10-6 cubic metre. One millilitre has the same volume, so the numerical value stays one.
Example 4: micrograms to kilograms
Metric prefixes attach to gram in mass unit names. One microgram is 10-6 gram, while one gram is 10-3 kilogram.
Example 5: Celsius to Fahrenheit
Temperature values need a scale and offset. Zero degrees Celsius converts exactly to 32 degrees Fahrenheit and 273.15 K. A temperature interval of 1 °C equals 1 K or 1.8 °F.
Exact Factors, Display Rounding and Significant Digits
SI prefix factors are exact powers of ten. Defined relations such as 1 litre = 10-3 cubic metre, 1 hectare = 104 square metres, 1 tonne = 1000 kilograms, 1 hour = 3600 seconds and 1 watt-hour = 3600 joules also have exact stated factors.
The calculator parses the entered decimal as an integer ratio and keeps conversions in rational arithmetic. This prevents ordinary binary floating-point artifacts such as displaying 0.30000000000000004 for a simple decimal operation. It also preserves mathematical values such as 5e-324 and 1e400 that fall outside ordinary JavaScript number handling.
A displayed answer may still be rounded to the selected number of significant digits. The result uses an equals sign only when the displayed decimal exactly represents the stored rational answer. Otherwise it uses an approximate sign. More output digits do not improve the quality of the original measurement.
Common Metric Conversion Mistakes
- Using a linear factor for area or volume. Convert square units with the squared prefix factor and cubic units with the cubed factor.
- Confusing M and m. M means mega, or 106. Lowercase m means milli, or 10-3.
- Using K for kilo. The kilo symbol is lowercase k. Uppercase K is the kelvin unit symbol.
- Attaching prefixes to kilogram. Mass prefixes attach to gram. A milligram is 10-3 gram, which equals 10-6 kilogram.
- Stacking prefixes. Write nanometre, not millimicrometre. One unit receives at most one SI prefix.
- Mixing temperature values and intervals. Temperature values need zero-point offsets. Temperature intervals do not.
- Treating mass as force. Grams and kilograms measure mass. Newtons measure force.
- Dropping unit context. A bare number does not show whether the factor applied to length, area, volume or another quantity.
Related Calculators
Frequently Asked Questions
What does this metric conversion calculator convert?
It converts SI prefixes and metric units for length, area, volume, mass, temperature, time, speed, acceleration, force, pressure, energy, power and frequency. Fahrenheit and Rankine appear only as temperature reference scales; broader U.S. customary and Imperial units stay outside this tool.
How do metric prefixes work?
Each SI prefix represents an exact power of ten. Kilo is 10 to the power of 3, centi is 10 to the power of -2, milli is 10 to the power of -3 and micro is 10 to the power of -6.
Does the calculator include all current SI prefixes?
Yes. It includes all 24 current prefixes from quetta at 10 to the power of 30 through quecto at 10 to the power of -30, including ronna, ronto and the two-character deca symbol da.
Why is 1 square centimetre equal to 0.0001 square metre?
One centimetre is 0.01 metre. Area uses two length dimensions, so the factor is squared: 0.01 multiplied by 0.01 equals 0.0001. A linear 0.01 factor would be incorrect for square units.
Is 1 cubic centimetre the same as 1 millilitre?
Yes. One cubic centimetre and one millilitre both equal exactly 0.000001 cubic metre. The calculator includes cubic-metre prefixes and litre prefixes in the same volume mode.
Why is 1 milligram not 0.001 kilogram?
The milli prefix attaches to gram. One milligram is 0.001 gram, and one gram is 0.001 kilogram. Therefore one milligram equals 0.000001 kilogram.
What is the difference between temperature and temperature interval conversion?
A temperature value has a scale and zero point, so Celsius and Fahrenheit conversions use offsets. A temperature interval measures a difference, so it uses scale factors only. A temperature interval of 1 °C equals 1 K or 1.8 °F.
Can I enter negative values and scientific notation?
Yes. Signed decimals and scientific notation are supported. Negative temperature values must still remain at or above absolute zero. Commas, fractions, unit symbols, formulas, Infinity and NaN are rejected.
Are metric conversion results exact?
The calculator uses exact stored definitions and exact decimal-rational arithmetic. The visible answer may be rounded to your selected significant digits, and the accuracy of a measured quantity still depends on the source measurement.
How is this different from a general unit conversion calculator?
This page focuses on SI units, accepted metric units and decimal prefixes. A general unit converter also connects metric values with U.S. customary, Imperial and other non-SI units, which may require additional definitions and variant labels.
Method and Official Sources
The SI system and prefix rules were checked against the BIPM SI Brochure, 9th edition, version 4.01 and the BIPM SI prefix table. Units accepted for use with SI were reviewed against NIST SP 330 Section 4. Defined quantity factors were checked against NIST SP 811 Appendix B.9. Temperature scales and exact reference points were checked against NIST SI temperature guidance.
Educational and measurement disclaimer: This calculator converts stated numerical values and defined unit factors. It does not measure a quantity, estimate uncertainty, calibrate an instrument, select a tolerable error or establish compliance with a laboratory, engineering, trade or legal requirement. Match displayed precision to the evidence in your source value.