Imagine trying to explain a recipe for a cake without the use of measurements. How much flour do you put in? A handful? What if my hand is bigger than yours? How much water do I put in? 2 jugs worth? What if we don’t have the same jug sizes? It all gets a bit messy – and I’m not talking about the cake!

Measurements are defined as the action of measuring something. Whether that’s size, distance, speed, time, weight, etc., we use measurements as it makes it easier to put things into perspective.

They are crucial to communicating and understanding the world around us. The only problem is that in different parts of the world, different measurement systems are used and it can get quite confusing. That’s why it’s good practice to know their differences and how to go from one unit to the other.

Therefore, in this article, we’ll explain the differences between the two main measurement systems, look at essential conversion factors, why it’s important to know them, and explore how to convert measurements between different units. Let’s jump in.

There are two main measurement systems in the world. There’s the metric system and the imperial system, both of which have different terms and units of measurement. The US uses the imperial system, whereas most of the world uses the metric system. Although they’ll both measure the same thing, the unit of measurement won’t be the same. For example, to measure length, some countries will use a larger unit of measurement, such as meters (metric). In contrast, others will use a smaller unit, such as feet (imperial). Both units work and refer to the same distance, but the measurement scale is different, which will give different values.

To someone who’s uninformed, it can seem like speaking a different language – and in some ways, they’re right – but if you’re familiar with both and can convert measurements between them, you’ll be able to understand what they mean. Also, it should be noted that the metric system is considered the international standard and is used heavily in science. Therefore, it’s essential for American students to learn it alongside the imperial system.

One of the measurement systems is the metric system – it is the official system of measurement in almost all countries around the world. It consists of measuring length in meters and centimeters, weight in grams and kilograms, and liquid volume in liters and milliliters.

The metric system adds prefixes to the original unit of measurement to distinguish between multiples of that unit. For instance, the prefix kilo is added to a unit of measurement to indicate a multiplication of 1,000 of that unit – 1 kilogram = 1,000 grams. The prefix milli is added to a unit of measurement to indicate a division of 1,000 of that unit – 1 liter = 1,000 milliliters. While metric prefixes can go up to multiplication and a division of a septillion, only a handful are used on a day-to-day basis.


The second main measurement system is the imperial system. It is the official system of measurement in only three countries – the United States of America, Liberia, and Myanmar. It consists of units such as pounds for weight, gallons for liquid volume, and feet and inches for length.

However, just because a country has an official measurement system, that doesn’t mean they don’t use the other one. For example, the United Kingdom officially uses the metric system. Still, they use miles to measure distance, an imperial measurement unit.

A conversion calculator is great for converting complicated measurements or units you aren't familiar with, but everyone should know a few key conversion factors when it comes to converting units of measurement. Whilst there are methods to convert units, it’s much easier to memorize each conversion factor and then work from there – you’ll be saving yourself a lot of time and effort. With that being said, the most important conversion factors are as follows:

  • Miles to Kilometers: 1 mile (mi) = 1.61 kilometers (km)
  • Pounds to Kilograms: 1 pound (lb) = 0.45 kilograms (kg)
  • Inches to Centimeters: 1 inch (in) = 2.54 centimeter (cm)
  • Feet to Meters 1 foot (ft) = 0.305 meters (m)
  • Square Feet to Square Meters: 1 (sq ft) = 0.0929 (sq m)
  • Ounces to Grams: 1 ounce (oz) = 28.3 grams (g)
  • US Gallons to Liters: 1 gallon (gal) = 3.785 liters (L)
  • Cups to Milliliters: 1 cup (c) = 240 milliliters (mL)
  • Fahrenheit to Celsius: F = (1.8 × C) + 32

Now that we know the conversion factors, we can use them as a foundation to easily do calculations for any unit conversion. Let’s look at practice problems in real-life scenarios to understand how to convert between metric units and imperial units.

How do I convert inches to centimeters?

Suppose you are looking for a new table top. You’ve sourced the wood you want, but it only comes in length units of 100 cm, 150 cm, and 200 cm. You can only fit a 50-inch table top in your kitchen, so you need to know which size to buy. But how many centimeters are 50 inches?

To work out which size wood you need to buy, you need to convert the tabletop, which is in centimeters, into inches. Or you can convert your 50-inch size requirement into centimeters. We do this so that we are working with the same units in the same measurement system.

We’ve established that 1 inch = 2.54 cm. Therefore, the first step is to multiply 50 inches by 2.54 cm to determine the size of the tabletop you need in cm.

  • 50 in × 2.54 cm = 127 cm

This means that you need a tabletop with a size of at least 127 cm. With this information, you can proceed to buy the 150 cm wood length and cut it down to 127 cm. But, what if you want to know how long you need to cut the wood in inches instead of cm?

By using the same conversion factor of 1 inch = 2.54 cm, you can divide the difference of 23cm (150 cm - 127 cm) by 2.54 to convert it into inches.

  • 23 cm ÷ 2.54 cm = 9.055 in

This means you need to cut the 150 cm piece of wood by 9.055 inches, or 23 cm, to reach the desired 50-inch tabletop length.

How do I convert miles into kilometers?

Let’s say you want to go for a run and you’re looking to hit a target of 10 kilometers. There’s a park next to your house, and so you decide to go for a run there. You know that one lap of the park is 2.5 miles, so how many laps of the park do you need to run to hit your 10 km target?

As in the previous example, you first want to change either the km into miles or miles into km so that you’re working with only one unit. Since you want to hit a target of 10 kilometers, it makes sense to change the miles into km as opposed to the other way around.

Using our unit conversions factor, we know that 1 mile = 1.61 km. The first step would be to find out the distance of a full lap around the park in kilometers. To do this, you can multiply 2.5 miles by 1.61 km.

  • 2.5 miles × 1.61 km = 4.025 km

This means that one full lap around the park is 4.025 km long. Using this, you can calculate how many laps you need to make. Since you want to run a total of 10 km, you then need to divide the total length you want to run (10 km) by the length of one lap (4.025 km).

  • 10 km ÷ 4.025 km = 2.48

The final answer of 2.48 means you must run for 2.48 laps around the park to hit your target of 10 km.

How do I convert pounds into kilograms?

Suppose you want to lose some weight for the summer, and you’ve hired a personal trainer for the next 12 weeks to guide you through the process. You currently way 185 lbs and want to lose 15 lbs over the next three months to hit your target of 170 lbs. But, your personal trainer is from the UK, where they don’t use pounds, and has asked for your weight loss goals in kilograms. What unit conversions would you need to do in order to give him the information he needs?

Again, first, you need to change units. In this scenario, you need to convert 185 lbs into kg. We know that 1 lb = 0.45 kg. Therefore, we need to multiply 185 lbs by 0.45 kg.

  • 185 lbs × 0.45 kg = 83.25 kg

Now you know how much you currently weigh in kg. The next step is calculating how much weight you want to lose. Since your goal is to lose 15 lbs, you can do the same thing you did in the previous step – multiply the lbs by 0.45 kg.

  • 15 lbs × 0.45 kg = 6.75 kg

This means you need to lose 6.75kg to hit your goal weight of 170 lbs. The final step is to do an extra calculation to check if we have got the right or wrong answer, which is to check if 170 lbs = 76.5 kg (83.25 kg - 6.75 kg)

  • 170 lbs × 0.45 kg = 76.5 kg

This confirms that you have converted the units correctly, and you can send these figures of your weight loss goals to your personal trainer.

How do I convert square feet to square meters?

Squared units look intimidating and can scare some people away. But, as long as you keep to the same principles discussed in the previous examples, it will work.

Say you live in a 950 sq ft big apartment, but it’s starting to feel a little cramped, and you want to move into a bigger apartment. You’ve been looking online and have found one you really like, but the size is advertised as 110 sq m. You want to know if 110 sq m is bigger than your current apartment and, if so, by how much.

Using our memorized conversion factors, we know that 1 sq ft = 0.0929 sq m. Since we’re working back from sq m to sq ft, you want to divide the 110 sq m by 0.0929 sq m instead of multiplying them together.

  • 110 sq m ÷ 0.0929 sq m = 1,184.06 sq feet

This means that the new apartment you’ve been looking at is 1,184 sq feet big, 234 sq feet bigger than your current apartment.

All the principles mentioned in these examples can be used to convert one unit of measurement into another, as long as you keep the conversion factors in mind.

How do I convert Fahrenheit to Celsius?

Converting Fahrenheit (F) to Celsius (C) works differently than the other examples shown. This is because the zero values for each don’t equate to the same thing. For instance, with miles and kilometers, zero for each means that there is no distance. Likewise with pounds and kilograms, zero indicates that there is no weight. However, when it comes to temperature, 0 Celsius, which is the freezing point, does not equal 0 Fahrenheit. Instead, it equates to 32 F.

In this case, there is a formula that we have to remember. The formula is as follows:

  • F = (1.8 × C) + 32

This means that 1 Fahrenheit is equal to 1.8 × the temperature in Celsius, plus 32. Let’s show this in an example.

Suppose you want to go on vacation to Paris, France. You’re planning on going in August during the first week of the month. You’ve looked at the weather forecast, and it says it will be 27 C the whole week. You’re not used to reading the temperature in Celsius and, therefore, need to convert it to Fahrenheit.

To do so, we simply have to plug in the celsius temperature into the equation.

  • (1.8 x 27 Celsius) + 32 = 80.6 Fahrenheit

This means that you can expect the temperature to be 80 Fahrenheit during your trip.

How many meters are in a kilometer?

The prefix kilo means to multiply the unit of measurement by 1,000. Therefore, there are 1,000 meters in a kilometer.

How many centimeters are in a meter?

The prefix centi means to divide the unit of measurement by 100. Therefore, there are 100 centimeters in a meter.

How many milliliters are in a liter?

The prefix milli means to divide the unit of measurement by 1,000. Therefore, there are 1,000 milliliters in a liter.

How many gallons are in a pint?

There are 8 pints in 1 gallon. This means that there is 1/8th of a gallon in a pint.

How many liters are in a gallon?

There are 3.785 liters in a gallon.