Converting Kilometers Per Hour to Miles Per Hour Formula and Tips

Understanding Metric and Imperial Units for Speed

When measuring speed, the most common units used around the world are kilometers per hour (km/h or kph) and miles per hour (mph). The metric system which uses kilometers is favored by most countries, while miles are still used in the United States, the UK, and a few other places.

This means that conversions between kph and mph are frequently needed for transportation, weather reports, athletic records, and other purposes. The formulas and values are easy enough, but can still cause confusion at times.

The Metric System

The metric system of measurement was introduced in the late 1700s and is based around the multiples of 10. Metric units such as meters, liters, and grams make conversions very simple by moving the decimal point.

Countries in Europe, Asia, Australia and many other parts of the globe have adopted the metric system. For issues of trade and transportation, weather tracking, and sporting events, using a standardized set of measurements just makes sense.

Imperial Units Still Used

However, imperial units including miles, inches, pounds, and so forth remain the standard across the UK, US and a couple other places. There is familiarity in society with speed limits set at 55 or 70mph, or hearing weather reports in Fahrenheit.

And so when discussing anything related to transportation or weather abroad, conversions between imperial and metric units are required on a regular basis.

Converting Kilometers to Miles - The Formula

The simplest means of converting a speed measured in kilometers per hour (kph) to miles per hour (mph) is to multiply it by 0.62137.

To demonstrate, here are some examples:

• 100 kph x 0.62137 = 62.137 mph
• 130 kph x 0.62137 = 80.778 mph
• 150 kph x 0.62137 = 93.206 mph

The 0.62137 figure is an exact conversion ratio. So whatever number in kilometers per hour you want to convert, you just need to multiply it by the factor.

Converting Smaller Numbers

That method works fine for simplicity, but the extra decimal places create issues if working with small numbers. For example, to convert 5 kph to mph, we would do:

5 kph x 0.62137 = 3.1069 mph

We don't really want all those extra decimal places. An alternative approach is to set up the numbers as a ratio:

(kph) / (1.609) = mph

Where 1.609 is the kilometer to mile ratio. So for our 5 kph example:

(5 kph) / (1.609) = 3.11 mph

Using the ratio approach results in fewer extra decimal places, making smaller number conversions simpler.

Larger Number Conversions

The 0.62137 factor and ratio approach will work equally well for large numbers. But an even easier tactic is possible by focusing on the numbers 100, 60 and 35. These can be used to quickly estimate kph to mph in your head.

To estimate converting kilometers per hour to miles per hour:

• 100 kph is roughly equal to 60 mph
• Each increase/decrease of 10 kph equals ~ 6 mph
• Each increase/decrease of 5 kph equals ~ 3 mph

So for example:

• 120 kph is approximately 20 kph above 100 kph
• 20 kph x the 6 mph ratio = 120 kph is about 72 mph

This shortcut allows fast mental math. It won't be perfectly precise but provides a ballpark figure. The exact formula or ratio method can then be applied if more accuracy is required.

Converting Miles to Kilometers

The same principles are applied when converting miles per hour to kph, just in the opposite order:

• The formula is mph x 1.609 = kph
• The ratio is (mph) / (0.62137) = kph
• Quick estimating can also be done based on 60 mph = ~100 kph

Converting Small Numbers

Again when working with smaller numbers, the ratio approach avoids unnecessary decimal places:

(10 mph) / (0.62137) = 16.09 kph

Larger Number Conversions

And the shortcut numbers can be used to compute a mental estimate:

• 55 mph x the 10 kph to 6 mph ratio = 55 mph is about 88 kph

Having an intuitive sense of these conversions is helpful for daily life. The exact formulas are there when precision is mandatory.

Converting Speed: Additional Notes

Metric Conversions Are Easier

As the metric system is formatted around units of 10, conversions between various measurements are more intuitive. While most countries utilize metrics for nearly everything, the persistence of imperial mph causes ongoing translation needs.

Always Double Check Yourself

Because speed limits and records will vary between reporting in mph or kph, it helps to double check any conversions. Small math errors can lead to dramatic errors related to driving safety and more.

Online tools make this easy to cross-reference your calculations. Don't rely entirely on mental estimating when precision matters.

Conversions Matter For Travel

When driving in a foreign country or planning an international trip, being aware of typical speed limits requires knowing conversions. Having a quick method to translate numbers will help avoid traffic violations or other issues.

Allow extra buffer room as well for unfamiliar units. Converting kph to mph takes practice to intuitively understand the relationships.

FAQs

What is the formula for converting kph to mph?

The formula is: kph x 0.62137 = mph

What is the ratio used to convert kph to mph?

The ratio used is: (kph) / (1.609) = mph

What numbers can I use for a quick/mental conversion?

Remember that 100 kph = ~60 mph. Then add or subtract ~6 mph for every 10 kph, and ~3 mph for every 5 kph.

Is it easier to convert metric or imperial measurements?

Metric conversions are easier since units scale by factors of 10. Imperial has more irregular relationships requiring exact formulas.