Metric prefixes scale SI units by powers of ten. This guide covers every standard prefix, how to convert between them without errors, why capitalization matters, and how they appear in everyday technology — from gigahertz processors to nanometer transistors.
Every time you check your phone's storage, read a processor spec sheet, or interpret a lab measurement, you are using metric prefixes. Kilo, mega, giga, milli, micro, nano — these prefixes appear in every technical field, from telecommunications to nanotechnology to data storage to electrical engineering. Yet a surprising number of professionals and students make consistent errors with them: confusing milli with mega, mishandling the factor-of-8 difference between megabits and megabytes, or struggling to convert between prefix tiers on the fly. This guide covers the complete set of SI prefixes from pico to tera (and beyond), explains how to convert between them using a reliable method that never fails, and shows exactly how they appear in the technologies you work with every day. Use the Metric Prefix Chart for a quick reference table, or the unit conversion workflows guide if you need a systematic conversion method for any unit pair.
Quick Reference
Metric prefixes scale SI units by powers of 10. The most common: kilo (k) = 10³, mega (M) = 10⁶, giga (G) = 10⁹, tera (T) = 10¹². Going down: milli (m) = 10⁻³, micro (µ) = 10⁻⁶, nano (n) = 10⁻⁹, pico (p) = 10⁻¹². Capitalization is significant — lowercase m = milli (10⁻³), uppercase M = Mega (10⁶).
Table 1: Full SI metric prefix table with symbol, factor, power of 10, and a real-world example for each. Source: International System of Units (SI), 9th edition (BIPM, 2019).
| Prefix | Symbol | Power of 10 | Factor | Real-World Example |
|---|---|---|---|---|
| Tera | T | 10¹² | 1,000,000,000,000 | 2 TB hard drive = 2 trillion bytes |
| Giga | G | 10⁹ | 1,000,000,000 | 4 GHz CPU = 4 billion cycles/second |
| Mega | M | 10⁶ | 1,000,000 | 100 Mbps connection = 100 million bits/sec |
| Kilo | k | 10³ | 1,000 | 1 km = 1,000 meters |
| Hecto | h | 10² | 100 | 1 hectare = 100 m × 100 m |
| Deka | da | 10¹ | 10 | 1 dekameter = 10 meters |
| (base) | – | 10⁰ | 1 | Meter, gram, second, ampere, etc. |
| Deci | d | 10⁻¹ | 0.1 | 1 dL = 0.1 liters (used in medicine) |
| Centi | c | 10⁻² | 0.01 | 1 cm = 0.01 meters |
| Milli | m | 10⁻³ | 0.001 | 500 mA = 0.5 amps |
| Micro | µ | 10⁻⁶ | 0.000001 | 100 µF capacitor |
| Nano | n | 10⁻⁹ | 0.000000001 | 7 nm transistor node |
| Pico | p | 10⁻¹² | 0.000000000001 | 10 pF capacitor |
| Femto | f | 10⁻¹⁵ | 10⁻¹⁵ | Femtosecond laser pulses |
Metric prefix symbols are case-sensitive by definition, and the distinction matters in practical use. The most dangerous pair:
m (lowercase) = milli = 10⁻³. As in: 500 mA (milliamps), 10 mH (millihenries), 100 ms (milliseconds).
M (uppercase) = Mega = 10⁶. As in: 100 MHz (megahertz), 50 MB (megabytes), 5 MW (megawatts).
Confusing these is not a minor formatting issue — it represents a factor of 10⁹ (one billion times) difference in magnitude. In electrical engineering, confusing mΩ (milliohms) with MΩ (megaohms) in a measurement would completely invalidate a diagnostic. Similarly, the Ohm's Law guide uses kΩ (kilohms) throughout — always lowercase k for kilo.
Other critical capitalization pairs: T (Tera, 10¹²) vs t (not a standard prefix). G (Giga) vs g (not a standard symbol). k (kilo) vs K (Kelvin — a unit, not a prefix).
This method works for any prefix-to-prefix conversion and requires no memorisation beyond knowing the powers of 10.
Table 2: Quick conversion reference for quantities you'll commonly encounter in electrical engineering and electronics. Each row shows the same quantity expressed at three prefix levels.
| Quantity | Micro (µ) | Milli (m) | Base Unit |
|---|---|---|---|
| Current (Ampere) | 1,000 µA | 1 mA | 0.001 A |
| Current (Ampere) | 1,000,000 µA | 1,000 mA | 1 A |
| Resistance (Ohm) | 1,000 µΩ | 1 mΩ | 0.001 Ω |
| Resistance (Ohm) | — | 1,000 mΩ | 1 Ω |
| Resistance (kΩ) | — | — | 1,000 Ω = 1 kΩ |
| Resistance (MΩ) | — | — | 1,000,000 Ω = 1 MΩ |
| Capacitance (F) | 1 µF | 0.001 mF | 0.000001 F |
| Capacitance (F) | 1,000 µF | 1 mF | 0.001 F |
Data storage: The gap between marketing and technical reality. Hard drive manufacturers define 1 GB = 10⁹ bytes (metric). Operating systems define 1 GiB = 2³⁰ bytes = 1,073,741,824 bytes (binary). A "1 TB" drive contains about 931 GiB. This is not deception — it is two legitimate but incompatible uses of the same prefix.
Network speed: Always in bits per second, not bytes. A 100 Mbps internet connection transfers 100 megabits per second = 12.5 megabytes per second. When downloading a 1 GB file (8 gigabits), a 100 Mbps connection takes about 80 seconds in theory, longer in practice. The Hz to kHz Converter shows the same prefix reasoning applied to frequency.
Processor technology: The "7nm" transistor node does not always literally mean 7 nanometers in any specific dimension — modern chip fabrication processes use the node name as a marketing identifier. A true 7 nm dimension is 7 × 10⁻⁹ meters, or 0.007 micrometers, or roughly 35 silicon atoms wide.
Power and energy: The kW to hp Converter works with kilowatts (kW = 10³ watts). A typical home uses 1–3 kW average continuous power, or about 720–2,160 kWh per month (kWh = kilowatt-hours, a unit of energy). Large power plants are rated in GW (gigawatts), and annual national energy consumption is measured in TWh (terawatt-hours).
Peta (P) = 10¹⁵, then Exa (E) = 10¹⁸, Zetta (Z) = 10²¹, and Yotta (Y) = 10²⁴. These are used in data science (petabytes of cloud data) and cosmology. The BIPM added Ronna (R, 10²⁷) and Quetta (Q, 10³⁰) to the official SI in 2022.
No — and this is a persistent source of confusion. In computing, 'kilo' traditionally meant 1,024 (2¹⁰) rather than 1,000, because binary systems work in powers of 2. The IEC introduced kibibyte (KiB, 2¹⁰) versus kilobyte (kB, 10³) to distinguish them formally. In practice, software and hardware manufacturers still mix both definitions.
Micro comes from the Greek word mikrós (small). The SI adopted µ (the Greek lowercase mu) as the prefix symbol. When µ is unavailable (as in some programming environments or ASCII-only text), it is commonly substituted with the letter 'u' — so 100uF means 100 µF in circuit schematics.
The prefix squares or cubes along with the unit. 1 km² = 1,000 m × 1,000 m = 1,000,000 m² (not 1,000 m²). 1 cm³ = 0.01 m × 0.01 m × 0.01 m = 10⁻⁶ m³. This trips up many students who apply the prefix factor once instead of applying it to each dimension. The unit conversion workflows guide covers this in detail.
Put the concepts above to work with these free, browser-based tools.
Metric prefixes are not optional knowledge in any technical field — they are the grammar of quantitative communication. A misread prefix represents a factor-of-a-billion error. The fix is simple: always check whether a symbol is upper or lower case, always verify whether a data value is in bits or bytes, and always track which power of 10 you are working with when converting. The Metric Prefix Chart gives you a wall-chart-ready reference table, and the unit conversion workflows guide provides a systematic conversion method you can apply to any unit regardless of prefix. For applying prefixes in real electrical calculations with kΩ and mA, the Ohm's Law guide walks through the full workflow. All articles in this cluster are linked from the Technical Guides hub.