Unit Converter
Convert length, weight, temperature, area, volume and speed instantly. Free online unit converter — metric, imperial, SI units. No signup required.
Unit Converter Tool
How to Use the Unit Converter
Select measurement category
Choose from Length, Weight, Temperature, Volume, Area or Speed using the category tabs at the top of the tool. The unit lists and quick conversions update instantly to match your selection.
Choose your units
Select the unit you're converting from and the unit you want to convert to using the two dropdown menus. Use the ⇄ swap button between them to instantly reverse the conversion direction.
Enter your value
Type the number in the input field. The result updates instantly as you type — no need to press any button. The formula line below the result shows the conversion relationship for reference.
Use quick conversions
Click any quick-conversion pill to instantly load a popular unit pair for your chosen category. This is the fastest way to do common conversions like km to miles or Celsius to Fahrenheit.
Metric vs Imperial — Why the World Can't Agree on Units
Why the World Uses Two Measurement Systems
The modern metric system was born out of the French Revolution. In 1799, France formally adopted the metre as a universal standard, defining it as one ten-millionth of the distance from the North Pole to the equator along a meridian passing through Paris. The vision was radical for its time: a measurement system based on nature, not on the length of a king's foot or the span of a nobleman's arm. Over the following two centuries, the metric system spread across Europe, Asia, Africa and South America, eventually forming the backbone of the modern International System of Units (SI).
Britain, which had colonised much of the world and exported its imperial system — pounds, feet, miles, gallons — formally adopted metric in 1965, though vestiges of imperial remain (road distances in miles, pints at the pub). The United States, however, never made the switch. Despite multiple official attempts — including the Metric Conversion Act of 1975 — public resistance and the enormous cost of infrastructure change kept America firmly in the imperial camp. Today, the USA, Myanmar, and Liberia are the only three countries that have not officially adopted the metric system as their primary standard.
The consequences of a divided world can be catastrophic. In 1999, NASA's Mars Climate Orbiter — a spacecraft costing US$125 million — was lost after it entered the Martian atmosphere at the wrong angle. The cause: one engineering team had used metric units (newton-seconds) while another used imperial (pound-force-seconds) for thruster data. The probe burned up, and the mismatch cost $125 million, months of mission planning, and irreplaceable scientific data. The scientific community has since doubled down on metric: all peer-reviewed research, all space agencies, and all international standards bodies use SI units without exception.
"In 1999, a $125 million Mars probe was lost because one team used metric units and another used imperial — the most expensive unit conversion error in history."
The Metric System in ASEAN: Singapore, Malaysia and Indonesia
All three of Southeast Asia's largest economies — Singapore, Malaysia, and Indonesia — officially use the International System of Units (SI) for government, commerce, science, and education. Children are taught metric in school from primary level. Weather is reported in Celsius, distances are measured in kilometres, and grocery items are weighed in grams and kilograms. On paper, the metric system is universal in this region.
In practice, imperial units persist in surprising pockets of everyday life, often as colonial-era legacies. In Singapore, the most striking example is property: the Housing Development Board (HDB) — which manages around 80% of Singapore's residential population — still lists flat sizes in square feet. A typical four-room HDB flat is described as 990 sq ft, not 92 m². Property portals, estate agents, and buyers all think in square feet, even though Singapore officially uses metric. The same is true of many private condominium listings.
In Malaysia, the construction and real estate industries similarly default to square feet for floor areas, while engineering and infrastructure projects follow metric. Older generations in Malaysia and Singapore often describe personal weight in pounds (and height in feet and inches), while hospital records and official documents use kilograms and centimetres. Indonesia's construction sector has largely standardised on metric, but traditional cooking recipes frequently call for local volume measures — the gelas (glass, roughly 200 ml) and sendok makan (tablespoon) — that sit alongside formal metric units.
These regional nuances make a unit converter more valuable in Southeast Asia than in countries where one system truly dominates. Whether you're buying a flat in Singapore, shipping goods from Jakarta, or comparing fuel economy between a Malaysian and a UK vehicle, the ability to switch fluently between metric and imperial is a practical daily skill.
Common Conversion Mistakes That Cost Businesses
Unit errors are not confined to space missions. In 1983, Air Canada Flight 143 — a Boeing 767 — ran out of fuel at 41,000 feet over Manitoba. The cause was a conversion error: ground crew calculated the required fuel in pounds but entered the quantity in kilograms, loading roughly half the fuel needed for the flight. The aircraft became a glider. Remarkably, the crew executed a successful emergency landing at a decommissioned airstrip in Gimli, Manitoba — earning the plane the nickname "the Gimli Glider." No lives were lost, but the incident became one of aviation's most studied case studies in unit error.
In pharmaceuticals, dosing errors caused by unit confusion can be fatal. Medical literature documents numerous cases where micrograms (mcg) were misread as milligrams (mg), delivering doses 1,000 times too large. International shipping routinely encounters weight limit disputes when freight is weighed in metric tonnes by one party and short tons (US) by another — the difference is approximately 10%, enough to cause customs delays or overloading penalties.
Practical steps to avoid unit errors in business and everyday life: always label units explicitly in contracts, spreadsheets, and purchase orders; never assume the other party uses the same system; use internationally recognised abbreviations (kg, lb, km, mi) rather than words alone; and when in doubt, specify both: "100 kg (220 lb)". For recipe conversions, note that US cups and UK cups are not identical, and that a US gallon and a UK gallon differ by nearly 20%.
10 Facts About Units of Measurement
The metre was originally defined as one ten-millionth of the distance from the North Pole to the equator — today it's defined by the speed of light.
Only three countries in the world still officially use the imperial system: the United States, Myanmar, and Liberia.
The 1983 "Gimli Glider" incident: Air Canada Flight 143 ran out of fuel mid-flight because technicians confused kilograms with pounds when calculating fuel load.
A nautical mile is exactly 1,852 metres and corresponds to one arc-minute of latitude — designed for navigation before GPS existed.
Singapore's HDB still lists flat sizes in square feet, even though Singapore officially uses the metric system.
The International System of Units (SI) defines 7 base units: metre, kilogram, second, ampere, kelvin, mole, and candela.
A US gallon (3.785 litres) and a UK gallon (4.546 litres) are different — a common source of confusion in recipes and fuel pricing.
Absolute zero (0 Kelvin, −273.15°C) is the coldest possible temperature — at this point, all molecular motion theoretically stops.
The Mach number is named after Austrian physicist Ernst Mach. Mach 1 is the speed of sound, approximately 343 m/s at sea level at 20°C.
Malaysia's construction industry uses a mix of metric and imperial units — floor areas are often quoted in square feet despite the metric system being official.
Frequently Asked Questions
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The metric system (SI) is a decimal-based system used by most of the world, built on base units like the metre, kilogram, and litre. The imperial system, used primarily in the USA, uses units like feet, pounds, and gallons — with non-decimal relationships (12 inches in a foot, 3 feet in a yard, 5,280 feet in a mile). Metric is the standard for science, engineering, and international commerce. Imperial persists in everyday life in the US and in some industries in former British colonies.
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To convert Celsius to Fahrenheit: multiply by 9/5 (1.8), then add 32. Formula: °F = (°C × 9/5) + 32. Example: 100°C = (100 × 1.8) + 32 = 212°F (water's boiling point). To go the other way — Fahrenheit to Celsius — subtract 32, then multiply by 5/9. Formula: °C = (°F − 32) × 5/9.
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One metre equals approximately 3.28084 feet (or more precisely, 3 feet 3.37 inches). Conversely, one foot equals 0.3048 metres — this is an exact defined value since 1959. A quick mental shorthand: multiply metres by 3.3 to get an approximate number of feet.
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A nautical mile is exactly 1,852 metres and corresponds to one arc-minute of latitude on Earth's surface. This relationship makes navigation by chart and compass extremely straightforward — a ship sailing one degree of latitude covers exactly 60 nautical miles. The unit remains the global standard for aviation and maritime navigation because it ties directly to Earth's geometry. Aircraft speed is measured in knots (nautical miles per hour) for the same reason.
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A US gallon is 3.785 litres, while a UK (imperial) gallon is 4.546 litres — roughly 20% larger. This matters in fuel pricing (a UK car's "mpg" figure looks better than a US car's because the gallon used is bigger), in recipe conversions, and in any context where liquid volume is specified without clarifying which gallon is meant. This converter uses the US gallon as the standard. If you need UK gallons, convert via litres.
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Absolute zero is −273.15°C (or 0 Kelvin, or −459.67°F). It is the theoretical lowest temperature possible — the point at which all molecular and atomic motion ceases. It has never been reached in practice, only approached. Experiments at MIT and NIST have cooled matter to within billionths of a Kelvin above absolute zero, producing exotic states of matter like Bose-Einstein condensates.
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Singapore's property market adopted square feet as its standard under British colonial rule, and the convention persisted after independence despite Singapore's official adoption of the metric system. The HDB — which manages over 80% of Singapore's residential housing — continues to publish floor areas in square feet, as do most private property agents and portals. This is primarily a market convention: buyers are accustomed to benchmarking price per square foot (psf), and changing the unit would require re-educating an entire market. To convert: 1 sq ft = 0.0929 m².
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To convert kilograms to pounds, multiply by 2.20462. Example: 70 kg × 2.20462 = 154.32 lb. A quick mental shorthand: multiply by 2.2 for an approximation. To go from pounds to kilograms, divide by 2.20462 (or multiply by 0.453592). Example: 154 lb ÷ 2.20462 ≈ 69.85 kg.
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Mach speed is a ratio of an object's speed to the local speed of sound. Mach 1 equals the speed of sound at the current air conditions — approximately 343 m/s (1,235 km/h or 767 mph) at sea level and 20°C. Mach 2 is twice that speed, and so on. The unit is named after Austrian physicist Ernst Mach (1838–1916). Because the speed of sound varies with altitude and temperature (it's about 295 m/s at cruise altitude), this converter uses the sea-level standard of 343 m/s.
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Most conversions are exact or accurate to at least 6 significant figures, based on NIST and SI definitions. A few notes: the foot is defined as exactly 0.3048 metres. The pound is defined as exactly 453.59237 grams. The Mach number uses the standard sea-level speed of sound (343 m/s at 20°C) — actual Mach speed varies with altitude and temperature. US gallon values use the US liquid gallon (3.785411784 litres). For legal or engineering use, always verify against the authoritative source (NIST, BIPM, or ISO) and use the full precision values.
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