Scientific Notation Converter

Type a number in any form — plain, with thousands separators, or already in E notation — and get it back four ways: scientific notation with one digit before the point, engineering notation with the exponent forced to a multiple of three, the machine-readable E form, and the fully written-out decimal. An optional significant-figures setting rounds all of them together. The default is the speed of light in metres per second, 299792458, which comes out as 2.99792458 × 10⁸ in scientific and 299.792458 × 10⁶ in engineering.

Engineering notation is the one people underuse. Holding the exponent to a multiple of three lines it up with the SI prefixes, so the reading tells you the unit directly: 10⁶ is mega, 10⁻³ is milli, 10⁻⁹ is nano. Scientific notation is tidier on paper; engineering is what you want when the number has to be spoken to someone or written on a part.

Two limits are worth knowing because neither announces itself. The number is parsed into a double, so anything needing more than about 17 significant digits is rounded before the tool ever sees it — enter 12345678901234567890 and what gets converted is 1.2345678901234567 × 10¹⁹, three digits short of what you typed. And the plain-decimal row is capped at twenty places after the point: 10⁻²⁰ still writes out in full, but 10⁻²¹ collapses to 0 in that row alone, while the other three stay correct.

Significant-figure rounding has the same double underneath, which is why it sometimes rounds the way you did not expect. Ask for three figures from 1.005 and you get 1.00, not 1.01 — the stored value is 1.0049999999999998934, so rounding down is the arithmetically correct answer for the number actually held, even though it is not the answer for the number you wrote.