SI Units, Prefixes and Base Quantities
International System of Units (SI) base units, derived units, and metric prefixes.
Overview
The International System of Units (SI) provides a standardized framework for measurement, defining base units for physical quantities. Prefixes are used with these units to denote multiples or submultiples, enabling the concise expression of very large or small values common in engineering and science.
The original source text is preserved here: "Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!" Prefixes used in the SI system in according with DIN 1301 "Units - Part 1: Unit names, unit symbols".
Key Formulas
While SI prefixes themselves are not formula-driven, converting between prefixed and base units follows a simple exponential relationship:
- Prefixed value = Base value times
10^(prefix exponent)
For example, to convert 5 kilometers (km) to meters (m): 5 km = 5 × 10³ m = 5000 m.
Variables
Symbols for common SI prefixes represent their scale factors:
- : kilo (10³)
- : mega (10⁶)
- : giga (10⁹)
- : tera (10¹²)
- : milli (10⁻³)
- : micro (10⁻⁶)
- : nano (10⁻⁹)
- : pico (10⁻¹²)
These are applied to SI base units like meter (m), second (s), or ampere (A).
Restored Original Source Tables
The following tables are restored from the original source page to preserve the complete reference data.
The restored source table below preserves the original Name of Factor and Decimal equivalent columns, including source-format prefix labels such as y - yokto, z - zepto, M - mega, and Y - yotta.
Decimal System Prefixes
Prefix | Name of Factor | Decimal equivalent | Exponential expression |
|---|---|---|---|
| y - yokto | septillionth | 0.000 000 000 000 000 000 000 001 | E-24 |
| z - zepto | sextillionth | 0.000 000 000 000 000 000 001 | E-21 |
| a - atto | trillionth | 0.000 000 000 000 000 001 | E-18 |
| f - femto | thousand billionth | 0.000 000 000 000 001 | E-15 |
| p - pico | billionth | 0.000 000 000 001 | E-12 |
| n - nano | thousand billionth | 0.000 000 001 | E-9 |
| μ - micro | millionth | 0.000 001 | E-6 |
| m - milli | thousandth | 0.001 | E-3 |
| c - centi | hundredth | 0.01 | E-2 |
| d - deci | tenth | 0.1 | E-1 |
| Uni | one | 1 | E0 |
| d - deka | ten | 10 | E1 |
| h - hecto | one hundred | 100 | E2 |
| k - kilo | one thousand | 1 000 | E3 |
| M - mega | one million | 1 000 000 | E6 |
| G - giga | one billion | 1 000 000 000 | E9 |
| T - tera | one trillion | 1 000 000 000 000 | E12 |
| P - peta | 1 000 000 000 000 000 | E15 | |
| E - exa | 1 000 000 000 000 000 000 | E18 | |
| Z - zetta | 1 000 000 000 000 000 000 000 | E21 | |
| Y - yotta | 1 000 000 000 000 000 000 000 000 | E24 |
Source: engineeringtoolbox.com
Original Source Layout/Search Table
The cached source page includes a non-engineering search/navigation table before the prefix content. It is documented here for strict source-table completeness and is not SI prefix data.
Cell 1 | Cell 2 | Cell 3 | Cell 4 | Cell 5 |
|---|---|---|---|---|
| x | x | Search | ||
| x |
Source: engineeringtoolbox.com
SI Prefix Converter
Prefixed Unit to Base Unit
Engineering Notes
- SI prefixes are strictly powers of 10, ensuring uniformity across all units and simplifying conversions.
- Always use the correct symbol case: 'k' for kilo (not 'K'), 'M' for mega, 'm' for milli, etc.
- In calculations, convert prefixed values to base units first to reduce errors, especially in mixed-unit equations.
- Prefixes like kilo, mega, and giga are often used in electrical engineering (e.g., kHz, MW), while milli, micro, and nano are common in precision contexts (e.g., mm, μF).
- Avoid non-standard or ambiguous prefixes; adhere to the official SI list for clarity and consistency.