Metric vs Imperial Units - Complete Comparison Guide 2025
Metric vs Imperial: Understanding the World's Measurement Systems
The metric system uses base-10 units (meters, kilograms, liters) while the imperial system uses feet, pounds, and gallons. 95% of the world uses metric; only the US, Liberia, and Myanmar use imperial. This guide explains both systems, which countries use what, and how to convert between them.
What is the Metric System?
The metric system, officially known as the International System of Units (SI), was developed in France during the French Revolution in the 1790s. It's designed around powers of 10, making conversions straightforward - you simply move the decimal point.
Key Metric Base Units:
- Length: Meter (m)
- Mass: Kilogram (kg)
- Volume: Liter (L)
- Temperature: Celsius (°C) or Kelvin (K)
Metric Prefixes
The metric system uses standard prefixes to indicate multiples of 10:
Larger Units
- kilo (k) = 1,000
- mega (M) = 1,000,000
- giga (G) = 1,000,000,000
Smaller Units
- centi (c) = 0.01
- milli (m) = 0.001
- micro (μ) = 0.000001
What is the Imperial System?
The imperial system evolved from various ancient measurement systems used in the British Empire. Unlike metric, imperial units don't follow a consistent pattern - there are 12 inches in a foot, 3 feet in a yard, and 1,760 yards in a mile.
Key Imperial Units:
- Length: Inch, Foot, Yard, Mile
- Mass: Ounce, Pound, Stone, Ton
- Volume: Fluid Ounce, Cup, Pint, Quart, Gallon
- Temperature: Fahrenheit (°F)
Convert Between Metric and Imperial Instantly
Use our free unit converter to switch between any metric and imperial units
Try Unit Converter →Which Countries Use Which System?
Countries Using Imperial System
Only three countries have not officially adopted the metric system:
- United States - Uses imperial for everyday life (miles, pounds, Fahrenheit)
- Myanmar (Burma) - Uses traditional Burmese units alongside some imperial
- Liberia - Historically used imperial due to American influence
Countries Using Metric System
The metric system is official in all other countries, including:
- All of Europe, Asia, Africa, and South America
- Canada (officially metric, but uses some imperial in daily life)
- United Kingdom (officially metric, but still uses miles for roads and pints for beer)
- Australia and New Zealand (fully metric since the 1970s)
Metric vs Imperial: Side-by-Side Comparison
| Aspect | Metric (SI) | Imperial |
|---|---|---|
| Base | Base-10 (decimal) | Various (12, 3, 16, etc.) |
| Length | Millimeter, Centimeter, Meter, Kilometer | Inch, Foot, Yard, Mile |
| Mass | Gram, Kilogram, Metric Ton | Ounce, Pound, Stone, Ton |
| Volume | Milliliter, Liter | Fluid Ounce, Cup, Pint, Gallon |
| Temperature | Celsius, Kelvin | Fahrenheit |
| Scientific Use | Universal standard | Rarely used |
| Conversion | Simple (multiply/divide by 10) | Complex (memorize factors) |
Common Metric to Imperial Conversions
Length
- 1 km = 0.62 miles
- 1 meter = 3.28 feet
- 1 cm = 0.39 inches
Weight
- 1 kg = 2.2 pounds
- 1 gram = 0.035 ounces
- 1 metric ton = 1.1 US tons
Volume
- 1 liter = 0.26 US gallons
- 1 liter = 4.23 cups
- 1 mL = 0.034 fluid ounces
Temperature
- 0°C = 32°F (freezing)
- 100°C = 212°F (boiling)
- 37°C = 98.6°F (body temp)
Why Does the US Still Use Imperial?
The United States nearly adopted the metric system several times but hasn't made a full switch for several reasons:
- Cost of conversion - Changing road signs, tools, and industrial equipment would cost billions
- Cultural familiarity - Americans are accustomed to imperial measurements
- No urgent need - The US economy functions well with imperial domestically
- Industry standards - Many US industries have established imperial specifications
Fun Fact:
US science, medicine, and military use metric units. NASA lost a $125 million Mars orbiter in 1999 due to a metric-imperial conversion error!
Conclusion
While the debate between metric vs imperial continues, the trend is clearly toward metric adoption worldwide. Understanding both systems - and being able to convert between them - is an essential skill in our globalized world.
Need to Convert Units?
Our free unit converter calculator makes metric-to-imperial conversions instant and accurate. Convert length, weight, temperature, volume, and more!
Try Unit Converter Free →