Unit prefix for 10-1 is deci, for 10-2 centi, for 10-3 milli, for 10-6 micro and so on. Powers greater or equal one also have names: 101 is deca, 102 is hecto, 103 is kilo etc..

We can say, for example, “Multiply the measurement in millimeters by 1000 and you have it in micrometers.”

But is there a prefix (even if it's just exotic) to express the zeroth power as an alternative to just using no prefix, like in “Divide the measurement in millimeters by 1000 and you get it in meters.”?

For example if we want to say it in a general way, it becomes pretty cumbersome: “Divide the measurement in milli by 1000 and you get the prefix-less unit itself.”


4 Answers 4


These are called base units. In SI Derived Unit, this Wikipedia article says

The International System of Units (SI) specifies a set of seven base units from which all other SI units of measurement are derived.

One could say,

Multiply the time in microseconds by 106 to obtain the base unit of seconds.


To obtain the base unit of meters, multiply the length in kilometers by 1000.

In the Wikipedia article on SI base unit, note that kilogram is the base unit. (One might expect gram to be the base unit, but it is not.)

  • The Wikipedia article refers to this one: en.m.wikipedia.org/wiki/SI_base_unit. It lists the base units as metre, kilogram, second, ampere, kelvin, mole, candela. Of the seven base units, only kilogram has a prefix. I'm editing my "base unit of grams" to use seconds instead.
    – rajah9
    Commented Feb 21, 2017 at 13:11

10o is 1, unity.

Thus you can just use unit in your sentences:

Multiply the measurement in millimetres by 1000 and you have it in micrometres*.
Divide the measurement in millilitres by 1000 and you get it in litres.

Divide the measurement in milli- by 1000 and you get the unit itself.

*This is slightly awkward because the more common term is micron.


The other answers are more appropriate. But supposing you are doing this mindlessly (or rather by an automated process) have a table of prefixes indexed by power. What you are looking for is the prefix for power = 0, the string that should be prepended to the unit measure.

That prefix is called the

null string

and is entered as


in your table and this works for most programming languages.


An exponent indicates the number of times a number is multiplied by itself: X2 = XX. A negative exponent indicates that the quantity is the denominator of a fraction in which the numerator is 1: X-2 = 1/XX.

Any number raised to the power of 0 is defined to be 1: x**0 = 1.

"Deci" means 10, centi means 100 and so on, but do not actually refer to exponents.

  • This doesn't go anywhere near answering the question, even if it were actually clear. Hint: use <sup></sup> to create superscripts.
    – Andrew Leach
    Commented Feb 20, 2017 at 14:47

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