Know the names, symbols and corresponding values for the decimal prefixes:

The idea

Decimal prefixes scale a base unit by powers of ten. Learn each name, its symbol and its value: kilo (k) = 10³ = 1000; mega (M) = 10⁶ = 1 000 000; giga (G) = 10⁹ = 1 000 000 000; tera (T) = 10¹² = 1 000 000 000 000; peta (P) = 10¹⁵ = 1 000 000 000 000 000. Apply them to units of information such as bytes and bits: 3 MB = 3 × 10⁶ bytes = 3 000 000 bytes, and 2 Gb = 2 × 10⁹ bits. To convert down a prefix, multiply by the value; to convert up, divide. For example, 5000 kB ÷ 1000 = 5 MB. Keep the symbol case correct: k is lower case, while M, G, T and P are upper case.

What earns the marks

• Kilo (k) = 10³ = 1000.
• Mega (M) = 10⁶ = 1 000 000.
• Giga (G) = 10⁹ = 1 000 000 000.
• Tera (T) = 10¹² = 1 000 000 000 000.
• Peta (P) = 10¹⁵ = 1 000 000 000 000 000.
• Correct conversion, e.g. 4 GB = 4 × 10⁹ bytes = 4 000 000 000 bytes.

Common mistakes and how to put them right

• Writing the symbol for kilo as an upper-case K.

  Put it right: The decimal prefix symbol for kilo is lower-case k, as in kB.

• Confusing mega and giga values, for example giving mega as 10⁹.

  Put it right: Mega = 10⁶ and giga = 10⁹.

• Dividing when converting from a larger prefix to a smaller one.

  Put it right: Converting from MB to kB multiplies by 1000, because there are 1000 kB in 1 MB.

• Using 1024 as the multiplier for decimal prefixes.

  Put it right: Decimal prefixes use powers of ten, so use 1000, 1 000 000 and so on.

Exam tips

• Write the power of ten beside each prefix before substituting numbers, so the scale is clear.
• Check the direction of the conversion: larger unit to smaller unit means multiply; smaller to larger means divide.
• Keep symbol case exact, since k, M, G, T and P are not interchangeable in meaning.