Convert Speed Units

Speed Dimensional Analysis

Speed describes the distance travelled over time. In other words, it represents how fast an object is moving.

The dimensional analysis stems from the interrelation of two other quantities: length and time.

Speed = length / time
      = L¹ / T¹
      = L¹ T⁻¹

where L and T represent the fundamental base units of length and time, respectively.

Commonly Used Speed Units

Speed is expressed by combining units of distance and time, resulting in multiple combinations, such as meters per second (m/s), miles per hour (mph), milimeters per year (mm/year), or inches per hour (in/h).

Among these units, meters per second (m/s) is the fundamental unit of speed in the metric system, which is widely used in scientific and engineering contexts.

However, m/s is rarely used in everyday life. In the nations using the metric system, kilometers per hour (km/h) is far more common. Similarly, regions adhering to the imperial system rely on miles per hour (mph) to express speed in familiar terms.

Why don't we use meters per second?

1. Human Speed Perception

When it comes to expressing speed quantities, we commonly use kilometers per hour (km/h) and miles per hour (mph). These units have become convenient and widely accepted due to their close relation to human speed perception and practicality in everyday life.

Our perception of speed is deeply connected to our own experiences and surroundings, particularly when we talk about traveling in vehicles. Imagine measuring the travel distance between two towns in millimeters or inches. It quickly becomes inconvenient and challenging to articulate such large numbers. Here are two everyday examples to illustrate this point.

• Option 1:

Last week, I drove 31,680,000 (thirty-one million six hundred eighty thousand) inches to visit my parents.

• Option 2:

Last week, I drove 500 (five hundred) miles to visit my parents.

Notice how saying the first sentence requires taking a pause to catch one's breath? Can you mentally add up the 1,584,000 inches or 25 miles you drove to visit your childhood friend in the nearby city? I'm sure you prefer the "500 + 25 miles" option, we feel more at ease with smaller numbers.

Similarly, the duration of these travels could be expressed in seconds or minutes. However, when we think of speed, the common distances we care about are typically in the order of hours. Let's revisit the previous example.

• Option 1:

Last week, I spent 32,400 seconds on the road to visit my parents.

• Option 2:

Last week, I spent 9 hours on the road to visit my parents.

Once again, expressing the duration in hours aligns with our daily experiences, as it is easier to relate to and comprehend. We move on foot or in vehicles like cars, bicycles, or trains, and we have a sense of how fast or slow we are traveling. Kilometers per hour and miles per hour are easily relatable to our daily experiences because they fall within a range that aligns with common speeds of human movement and land-based transportation.

2. Speed Quantities Historical Convention

The historical convention of using kilometers per hour (km/h) and miles per hour (mph) as standard units for measuring vehicular speeds has deep roots in human civilization. These units gained prominence during the 19th and 20th centuries with the evolution of the transportation industry, where the need for a universally understood and standardized speed unit became crucial. The established regulations and standards, such as speed limit signs and vehicle speedometers, further solidified the usage of km/h and mph in various countries.

Furthermore, the global consistency and cultural influences play a significant role. While the metric system, including meters per second, is common in scientific and technical contexts, kilometers per hour and miles per hour have become a cultural norm in different regions. Their widespread usage facilitates international communication and agreements.

Overall, the familiarity, consistency, and practical advantages of kilometers per hour and miles per hour have led to their continued widespread usage for expressing vehicular speeds, while the transition to alternative units would require significant effort and resistance to change.

3. Kilometers per Hour and Miles per Hour in Everyday Life

As we discussed earlier, given their convenience and historical significance, the speed units of km/h and mph are ubiquitous in various aspects of everyday life. Some examples include:

• Speed limits on road signs, and speedometers in vehicles.
• Exercise equipment, like treadmills, stationary bikes, and elliptical machines.
• Wind reports in weather forecastas.
• Running speed displays in smartwatches.

Which countries use miles per hour (mph)?

The use of miles per hour (mph) as the standard unit for measuring speed is prevalent in countries that have not adopted the metric system. These countries often use the imperial system of units, which includes miles, feet, and inches, as opposed to the metric system, which uses kilometers, meters, centimeters, and milimiters. Here are the countries that use mph instead of km/h:

• United States: In the United States, mph is the standard unit for measuring speed on road signs, speedometers, and in official communications.

• United Kingdom: While the UK has largely transitioned to the metric system, miles per hour is still used for measuring speed and distance in road signs and many transportation-related applications.

• Canada: Canada uses the metric system for most measurements but still uses mph for speed limits and some road signs, particularly in areas close to the US border.

• Liberia: Liberia, located in West Africa, also uses mph due to its historical ties with the United States.

• Myanmar (Burma).

• Some Caribbean Nations: Several countries in the Caribbean, including the Bahamas, Belize, and Jamaica, use mph for speed measurements.

It's important to note that some of these countries may use a combination of mph and km/h, especially in contexts related to international travel and in scientific or technical applications. However, for general day-to-day use, mph remains the primary unit for measuring speed in these countries.

Common Speed Values

Here you'll find a list of speed references to effectively compare orders of magnitude.

Speed in Sports

Speed of Cars, Trains, Planes and Other Vehicles

Speed in Animals and Nature