## Conversion formula

The conversion factor from kilometers to millimeters is 1000000, which means that 1 kilometer is equal to 1000000 millimeters:

1 km = 1000000 mm

To convert 421 kilometers into millimeters we have to multiply 421 by the conversion factor in order to get the length amount from kilometers to millimeters. We can also form a simple proportion to calculate the result:

1 km → 1000000 mm

421 km → L(mm)

Solve the above proportion to obtain the length L in millimeters:

L(mm) = 421 km × 1000000 mm

L(mm) = 421000000 mm

The final result is:

421 km → 421000000 mm

We conclude that 421 kilometers is equivalent to 421000000 millimeters:

421 kilometers = 421000000 millimeters

## Alternative conversion

We can also convert by utilizing the inverse value of the conversion factor. In this case 1 millimeter is equal to 2.375296912114E-9 × 421 kilometers.

Another way is saying that 421 kilometers is equal to 1 ÷ 2.375296912114E-9 millimeters.

## Approximate result

For practical purposes we can round our final result to an approximate numerical value. We can say that four hundred twenty-one kilometers is approximately four hundred twenty-one million millimeters:

421 km ≅ 421000000 mm

An alternative is also that one millimeter is approximately zero times four hundred twenty-one kilometers.

## Conversion table

### kilometers to millimeters chart

For quick reference purposes, below is the conversion table you can use to convert from kilometers to millimeters

kilometers (km) millimeters (mm)
422 kilometers 422000000 millimeters
423 kilometers 423000000 millimeters
424 kilometers 424000000 millimeters
425 kilometers 425000000 millimeters
426 kilometers 426000000 millimeters
427 kilometers 427000000 millimeters
428 kilometers 428000000 millimeters
429 kilometers 429000000 millimeters
430 kilometers 430000000 millimeters
431 kilometers 431000000 millimeters