421 miles per hour in kilometers per hour

Conversion

421 miles per hour is equivalent to 677.533824 kilometers per hour.^[1]

Conversion in the opposite direction

The inverse of the conversion factor is that 1 kilometer per hour is equal to 0.00147594107419794 times 421 miles per hour.

It can also be expressed as: 421 miles per hour is equal to $\frac{1}{0.00147594107419794}$ kilometers per hour.

Approximation

An approximate numerical result would be: four hundred and twenty-one miles per hour is about six hundred and seventy-seven point five two kilometers per hour, or alternatively, a kilometer per hour is about zero times four hundred and twenty-one miles per hour.

Units involved

This is how the units in this conversion are defined:

Miles Per Hour

"Miles per hour (abbreviated mph, MPH or mi/h) is an imperial and United States customary unit of speed expressing the number of statute miles covered in one hour. Although kilometres per hour is now the most widely used measure of speed, miles per hour remains the standard unit for speed limits in the United States, the United Kingdom, Antigua & Barbuda and Puerto Rico, although the latter two use kilometres for long distances."

Wikipedia page of miles per hour

Kilometers Per Hour

"The kilometer per hour is a unit of speed, expressing the number of kilometres travelled in one hour. The unit symbol is km/h. Worldwide, it is the most commonly used unit of speed on road signs and car speedometers."

Wikipedia page of kilometers per hour

Footnotes

[1] The precision is 15 significant digits (fourteen digits to the right of the decimal point).

Results may contain small errors due to the use of floating point arithmetic.