I recently came across this page with someĀ formulas for converting miles to kilometers. There is one that’s simple enough to do in your head:

Divide the number of miles by five and subtract that from the original. Then double the resulting number.

So I started by converting some of the speed limits from around town:

mph |
km/h |

40 | 64 |

45 | 72 |

65 | 104 |

70 | 112 |

That’s when I noticed something interesting. When you add 5 to the miles per hour being converted, its metric equivalent goes up by 8. In other words, **whenever a speed in miles per hour is a multiple of 5, its corresponding kilometers per hour will be a multiple of 8.** Mind blowing or what. It’s then that a pattern begins to form and all of a sudden, understanding kilometers becomes less intimidating.

mph |
km/h |

5 | 8 |

10 | 16 |

15 | 24 |

20 | 32 |

25 | 40 |

30 | 48 |

35 | 56 |

40 | 64 |

45 | 72 |

50 | 80 |

And so the pattern continues towards an easier way to understand the metric system.