Measurement, units of measurement, and conversions. METRIC RULES!

Unit Prefixes

The following table lists the prefixes for decimal powers.

Number Multiple Prefix Symbol Cardinal
US/International
Note
1 000 000 000 000 000 000 000 000 1e+24 yotta Y septillion/quadrillion yotta = Greek for 8 = 1000^8
1 000 000 000 000 000 000 000 1e+21 zetta Z sextillion/-- zetta = sept = French for 7 = 1000^7
1 000 000 000 000 000 000 1e+18 exa E quintillion/trillion exa = Greek for 6 = 1000^6
1 000 000 000 000 000 1e+15 peta P quadrillion/--  
1 000 000 000 000 1e+12 tera T trillion/billion  
1 000 000 000 1e+09 giga G billion/milliard  
1 000 000 1e+06 mega M million  
1 000 1e+03 kilo k ⇒ K thousand  
100 1e+02 hecto h ⇒ H hundred  
10 1e+01 deka da ⇒ D ten  
1 1e±00        
0.1 1e-01 deci d    
0.01 1e-02 centi c    
0.000 1 1e-03 milli m    
0.000 000 1 1e-06 micro μ    
0.000 000 000 1 1e-09 nano n    
0.000 000 000 000 1 1e-12 pico p    
0.000 000 000 000 000 1 1e-15 femto f    
0.000 000 000 000 000 000 1 1e-18 atto a   atto = atten = Greek for 18
0.000 000 000 000 000 000 000 1 1e-21 zepto z   zetta = sept = French for 7 = 1/1000^7
0.000 000 000 000 000 000 000 000 1 1e-24 yocto y   yocto = Greek for 8 = 1/1000^8

Hecto (102), deka (10-1), deci (10-1), and centi (10-2) are the only prefixes that are not powers of 103 or 10-3. They are uncommon except for c (centi) which is only commonly used with meter, as in 1 cm = 10-2 m.

The SI symbols should be consistent with case but the official standard does not do this. Positive powers should be uppercase and negative powers lowercase. "k" should be "K", "h" should be "H", and "da" is outright clumsy and should be "D". This practice is officially done with Z & z, as well as Y and y. Since this is my website, I will, as of this day [2004-08-16], make it the law on my site!

The symbol for micro (μ) is somewhat clumsy since it isn't an ASCII character but at least it's an ANSI character (181, xB5) and at least it's a lowercase mu (μ, 956, x3BC) instead of an uppercase Mu (Μ, 924, x39C).

See also Numbers.

Miscellany

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