Convert any number to a coefficient-and-exponent pair, and see the metric prefixes those exponents map to.
Computed in your browser from the number above.
Scientific notation writes a number as a coefficient between 1 and 10, multiplied by a power of 10. It's a compact way to express very large or very small numbers without a long string of zeros.
To go back the other direction, multiply the coefficient by 10 raised to the exponent. A negative exponent means the number is smaller than 1, such as 4.5 x 10^-4 = 0.00045.
Every common metric prefix is just scientific notation at a fixed, named exponent, the same table NIST publishes for the International System of Units:
Enter 123000000 above and the exponent field will read 8, one short of the "mega" mark at 10^6, since 1.23 x 10^8 isn't a round multiple of a named prefix; prefixes only land exactly on multiples of three.
Rounding down (a floor operation on the base-10 logarithm) is what keeps the coefficient between 1 and 10, which is the definition of proper scientific notation. Rounding to the nearest exponent instead would sometimes push the coefficient below 1 or up to 10, breaking that convention.
The calculator returns a plain 0 rather than trying to force it into a coefficient-and-exponent form. Zero has no meaningful scientific notation, since the logarithm step that finds the exponent is undefined at zero.
Yes, just a different way of writing it down. 1.23456e5 and 1.23456 times 10 to the 5th power mean exactly the same number; E notation exists because calculators and plain text can't easily print a raised exponent, so the letter E stands in for "times ten to the power of."
Metric prefixes are scientific notation with a name attached to specific round exponents. Kilo always means times 10 to the 3rd, milli always means times 10 to the negative 3rd, regardless of what's being measured; the reference table above lists the common ones.