Unit Converter

What are the most common metric to imperial unit conversions?

Unit conversion is the process of changing a measurement from one unit to another within the same measurement category. This calculator supports four major categories: length, weight, volume, and speed, covering both metric and imperial systems used worldwide. — also see our temperature converter. — also see our hex converter. Use the currency converter for related calculations. See also: the Length Converter and the Weight Converter.

Length Conversions

Length is one of the most frequently converted measurement types. The metric system uses meters as its base unit, with kilometers for large distances and centimeters or millimeters for small measurements. The imperial system uses inches, feet, yards, and miles. Common conversions include: 1 mile equals 1.609 kilometers, 1 foot equals 0.3048 meters, and 1 inch equals 2.54 centimeters. These conversions are essential for international travel, construction, and everyday measurements.

Weight Conversions

Weight conversion is frequently needed when comparing products internationally or following recipes from different countries. The metric system uses grams and kilograms, while the imperial system uses ounces and pounds. Key conversions include: 1 kilogram equals 2.205 pounds, 1 pound equals 453.6 grams, and 1 ounce equals 28.35 grams. For larger weights, 1 metric ton equals 1,000 kilograms or approximately 2,205 pounds.

Volume Conversions

Volume measurements vary significantly between metric and imperial systems. The metric system uses liters and milliliters, while the imperial system uses gallons, quarts, cups, and fluid ounces. Important conversions include: 1 gallon equals 3.785 liters, 1 cup equals 236.6 milliliters, and 1 fluid ounce equals 29.57 milliliters. These conversions are particularly useful for cooking, baking, and understanding product sizes across different countries.

Speed Conversions

Speed conversion is important for understanding speed limits, wind speeds, and athletic performance across different measurement systems. Common conversions include: 1 mile per hour (mph) equals 1.609 kilometers per hour (kph), 1 knot equals 1.852 kph, and 1 meter per second equals 3.6 kph. Understanding these conversions helps when driving in foreign countries or interpreting weather reports from international sources.

Why does unit conversion matter?

Units of measurement define how we quantify the physical world — length, mass, temperature, volume, area, speed, and more. Different countries, industries, and historical periods have used different unit systems, creating a persistent need for conversion. The United States primarily uses the US customary system (derived from imperial). Most of the world uses the International System of Units (SI/metric). India uses metric for most purposes, but imperial units appear in construction (feet, inches), screen sizes (inches), and everyday speech.

Errors in unit conversion have caused spectacular real-world failures: the 1999 Mars Climate Orbiter crash (metric vs imperial thrust data), a 1983 Air Canada flight that ran out of fuel mid-flight (pounds vs kilograms for fuel calculation), and numerous medical dosing errors when mg/kg is confused with mg/lb.

What is the metric system and how do SI units work?

The International System of Units (SI) is built on seven base units from which all other units are derived:

• Metre (m): Length
• Kilogram (kg): Mass
• Second (s): Time
• Ampere (A): Electric current
• Kelvin (K): Temperature
• Mole (mol): Amount of substance
• Candela (cd): Luminous intensity

The metric system uses decimal prefixes to scale units: kilo (10³), mega (10⁶), giga (10⁹), centi (10⁻²), milli (10⁻³), micro (10⁻⁶). This makes conversion within the metric system simply a matter of moving the decimal point.

Length conversion quick reference

• 1 km = 1,000 m = 0.621 miles = 3,280.8 feet
• 1 m = 100 cm = 3.281 feet = 39.37 inches
• 1 mile = 1.609 km = 1,760 yards = 5,280 feet
• 1 foot = 30.48 cm | 1 inch = 2.54 cm

Weight/mass conversion quick reference

• 1 kg = 1,000 g = 2.205 pounds = 35.27 ounces
• 1 pound = 453.6 g = 16 ounces
• 1 stone = 14 pounds = 6.35 kg
• 1 tonne = 1,000 kg = 2,204.6 pounds

Volume conversion quick reference

• 1 litre = 1,000 ml = 0.264 US gallons = 1.057 US quarts
• 1 US gallon = 3.785 litres = 4 quarts = 8 pints = 128 fluid ounces
• 1 UK gallon = 4.546 litres (different from US gallon)
• 1 tablespoon (tbsp) = 15 ml | 1 teaspoon (tsp) = 5 ml | 1 cup = 240 ml

Area conversion quick reference

• 1 m² = 10.764 square feet = 1.196 square yards
• 1 acre = 4,047 m² = 43,560 sq ft ≈ 0.405 hectares
• 1 hectare = 10,000 m² = 2.471 acres
• 1 square kilometre = 100 hectares = 0.386 square miles

Speed conversion quick reference

• 1 km/h = 0.278 m/s = 0.621 mph
• 1 mph = 1.609 km/h = 0.447 m/s
• 1 knot = 1.852 km/h = 1.151 mph (used in aviation and maritime)
• Speed of light = 299,792 km/s = 670,616,629 mph

Frequently asked questions about unit conversion

What is the easiest way to convert km to miles? Multiply by 0.621 for an accurate result. A quick mental shortcut: multiply by 5 and divide by 8 (or multiply by 0.625). For example, 80 km: 80 × 5 = 400 ÷ 8 = 50 miles (actual: 49.7 miles — close enough for practical use).

How do I convert Celsius to Fahrenheit? °F = (°C × 9/5) + 32. For a quick mental approximation: double the Celsius and add 30 (gives ±2°F for temperatures between 0°C and 30°C). 20°C: exact = 68°F, approximation = 70°F.

Why are there two different gallons (US and UK)? The US gallon (3.785 litres) and the UK/Imperial gallon (4.546 litres) diverged historically after American independence. The US retained older measurement standards while Britain reformed its system. Always specify US or UK when gallon precision matters — the difference is approximately 20%.

Most common unit conversions — quick reference