Mathwords logoMathwords

Peta- — Definition, Formula & Examples

Peta- is a metric (SI) prefix that means 101510^{15}, or one quadrillion. Its symbol is P, so 1 petabyte (PB) equals 1,000,000,000,000,0001{,}000{,}000{,}000{,}000{,}000 bytes.

In the International System of Units (SI), peta- denotes multiplication by 101510^{15}. Adopted in 1975 by the General Conference on Weights and Measures, it occupies the fifth position above the base unit on the large-prefix scale: kilo (10310^{3}), mega (10610^{6}), giga (10910^{9}), tera (101210^{12}), peta (101510^{15}).

Key Formula

1  P(unit)=1015  (unit)1\;\text{P(unit)} = 10^{15}\;\text{(unit)}
Where:
  • PP = The SI symbol for peta-, placed before the unit symbol
  • 101510^{15} = The multiplier, equal to 1,000,000,000,000,000 (one quadrillion)

How It Works

Attach "peta-" to any SI unit to multiply that unit by 101510^{15}. For instance, 1 petameter (Pm) equals 101510^{15} meters. To convert from a peta-unit to the base unit, multiply by 101510^{15}. To convert from the base unit to a peta-unit, divide by 101510^{15}. You move the decimal point 15 places when converting.

Worked Example

Problem: A data center stores 3.2 petabytes (PB) of data. How many gigabytes (GB) is that?
Step 1: Write each prefix as a power of 10.
1  PB=1015  B,1  GB=109  B1\;\text{PB} = 10^{15}\;\text{B}, \quad 1\;\text{GB} = 10^{9}\;\text{B}
Step 2: Find how many GB fit in one PB by dividing the powers.
1015109=106⇒1  PB=106  GB\frac{10^{15}}{10^{9}} = 10^{6} \quad\Rightarrow\quad 1\;\text{PB} = 10^{6}\;\text{GB}
Step 3: Multiply by 3.2.
3.2×106  GB=3,200,000  GB3.2 \times 10^{6}\;\text{GB} = 3{,}200{,}000\;\text{GB}
Answer: 3.2 PB = 3,200,000 GB (3.2 million gigabytes).

Why It Matters

Peta- appears most often in computing and astronomy. Global internet traffic is measured in petabytes per month, and stellar distances can reach petameters. Understanding this prefix helps you read scientific data without being overwhelmed by strings of zeros.

Common Mistakes

Mistake: Confusing peta- (101510^{15}) with the binary "pebi-" prefix (250=1,125,899,906,842,6242^{50} = 1{,}125{,}899{,}906{,}842{,}624).
Correction: In SI, peta- always means exactly 101510^{15}. The binary equivalent, pebi- (Pi), is about 12.6% larger. Use PB for 101510^{15} bytes and PiB for 2502^{50} bytes.

Related Terms