Unit Converter

Convert length, weight, temperature, data, speed, and area with one tool.

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📖 How Unit Converter Works

Unit conversion is an essential skill across science, engineering, cooking, travel, fitness, and everyday life. Whether you're converting kilometers to miles for a road trip abroad, kilograms to pounds for a recipe, or Celsius to Fahrenheit to understand a foreign weather report, having a fast, accurate, and multi-category converter prevents errors and saves time. This converter handles six distinct categories — length, mass, temperature, data storage, speed, and area — all in one unified interface.

How Unit Conversion Works

Result = Input × (From Unit Factor ÷ To Unit Factor)

Each unit is expressed as a conversion factor relative to a shared base unit. For length, the base is meters. To convert 5 km to miles: 5 × 1,000 (m/km) ÷ 1,609.344 (m/mi) = 3.107 miles. This same pattern works for mass (base: kg), speed (base: m/s), area (base: m²), and data (base: bytes).

Quick Conversion Reference

  • Length: 1 mile = 1.609 km | 1 inch = 2.54 cm | 1 foot = 0.3048 m | 1 yard = 0.914 m
  • Mass: 1 lb = 0.4536 kg | 1 oz = 28.35 g | 1 stone = 6.35 kg | 1 metric ton = 2,205 lbs
  • Speed: 60 mph = 96.56 km/h | 1 m/s = 3.6 km/h | 1 knot = 1.852 km/h
  • Area: 1 acre = 4,047 m² | 1 hectare = 2.471 acres | 1 mi² = 640 acres

Temperature: The Special Case

Temperature conversion is unique — it requires both multiplication and offset because the three scales (Celsius, Fahrenheit, Kelvin) have different zero points:

  • °C to °F: (°C × 9/5) + 32 | e.g., 100°C = 212°F (boiling water)
  • °F to °C: (°F − 32) × 5/9 | e.g., 72°F ≈ 22.2°C (room temperature)
  • °C to K: °C + 273.15 | e.g., 0°C = 273.15 K (freezing point)
  • Absolute Zero: 0 K = −273.15°C = −459.67°F — the lowest physically possible temperature.

Kelvin is the SI base unit of temperature. It is used in scientific and engineering contexts (e.g., the Ideal Gas Law, blackbody radiation calculations) because it never goes negative, making mathematical relationships cleaner.

Data Storage: Binary vs. Decimal Prefixes

Digital data uses binary prefixes: 1 Kilobyte (KB) = 1,024 Bytes. This matters practically — hard drive and SSD manufacturers advertise storage using decimal prefixes (1 KB = 1,000 B), while operating systems display it in binary. A 1 TB hard drive marketed by the manufacturer contains 1,000,000,000,000 bytes, but your OS reports it as ~931 GiB. This is why "usable" storage always seems less than advertised — not a manufacturer trick, just a unit mismatch.

Metric vs. Imperial: A Brief History

The metric system was developed during the French Revolution in the 1790s to replace the chaotic tangle of local units used across Europe. By the late 20th century, it had been adopted by essentially every country in the world as the standard for science, trade, and everyday life — with three notable exceptions: the United States, Myanmar, and Liberia, which still primarily use customary/imperial units for everyday life. The US officially adopted the metric system as legal in 1866 and signed the Metre Convention in 1875, but consumer adoption has remained slow due to cultural inertia.

Speed Units in Context

  • mph (miles per hour): Standard in the US and UK for road speeds.
  • km/h (kilometers per hour): Standard in most of the world for road speeds.
  • Knots (nautical miles/hr): Used in aviation and maritime navigation worldwide.
  • Mach: Ratio of speed to the local speed of sound (~340.29 m/s at sea level). Mach 1 ≈ 767 mph. Used for aircraft and projectiles.
  • m/s: The SI base unit for speed, used in physics and engineering.
❓ What is the metric system?

The International System of Units (SI) uses base-10 prefixes for straightforward scaling: milli (×0.001), centi (×0.01), kilo (×1,000), mega (×1,000,000), giga (×1,000,000,000). It is the official measurement system for 194 countries and all scientific disciplines. The US uses metric exclusively in science, medicine, the military, and international trade.

❓ What is a nautical mile?

A nautical mile (1,852 meters) is defined as one minute (1/60 of a degree) of arc of latitude along any meridian. Since the Earth's circumference is divided into 360 degrees of latitude × 60 minutes each = 21,600 nautical miles, this gives navigators a direct relationship between angle and distance on the globe. A "knot" is one nautical mile per hour.

❓ Why does 1 km not equal exactly 0.6 miles?

One kilometer = exactly 0.621371192 miles. The conversion is not a round number because the mile was defined historically (1 mile = 5,280 feet; 1 foot = 0.3048 meters exactly) without any intention to align with the metric system. The conversion factor is irrational relative to the metric base units.

❓ How many square feet are in an acre?

Exactly 43,560 square feet (or 4,840 sq yd, or 4,047 m²). An acre was historically defined as the amount of land a yoke of oxen could plow in one day. A "square acre" would be approximately 208.7 ft × 208.7 ft. A US football field (including end zones) is about 1.32 acres.

❓ What's the difference between a US ton and a metric ton?

A US short ton = 2,000 lbs (907.2 kg). A metric ton (tonne) = 1,000 kg = 2,204.6 lbs. A British long ton = 2,240 lbs (1,016 kg). When purchasing materials in bulk or interpreting shipping weights, it's important to confirm which "ton" is meant — the difference can be 10% or more.