How this calculator works
Scientific notation uses one digit before the decimal point. Engineering notation instead uses an exponent divisible by three, so a non-zero coefficient has magnitude at least one and below one thousand. Rounding happens before grouping, which carries 999.999 into the next group when necessary. Trailing zeros in the notation retain the selected significant figures. Numeric inputs keep about 15 to 17 significant digits.
Formula
x = c × 10^e, where e is a multiple of 3 and 1 ≤ |c| < 1000. If scientific notation is m × 10^p, set e = 3 floor(p/3) and c = m × 10^(p-e), after rounding.
Worked example
12345 to four significant figures becomes 12.35 × 10³, which corresponds to the kilo prefix. -0.0000456 to three figures becomes -45.6 × 10^-6, using micro. Rounding 999999 to three figures gives 1.00 × 10⁶.
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Frequently asked questions
Why does a negative exponent round down to a group?
Grouping uses the mathematical floor. For a scientific exponent of -5, the engineering group is -6, putting the coefficient between 1 and 1000.
Do all engineering exponents have an SI prefix?
No. The table covers the official three-step prefixes from 10^-30 to 10^30. More extreme numbers still have engineering notation.
What about zero?
Zero has no unique exponent. This tool uses 0 × 10⁰ and no prefix.
Can I attach a prefix to kilograms?
Mass prefixes attach to gram, so 10^-6 kg is 1 mg. Choose the underlying unit before applying the prefix shown here.