Conversion Calculator
Convert any unit instantly — length, weight, temperature, volume, area, speed, time, and pressure. Bidirectional, live, with full unit panels. No button press needed.
Length — All Units
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Common Conversion Factors
The most-used conversions at a glance.
| Category | Conversion Factor | Example | Reverse |
|---|---|---|---|
| Miles → km | × 1.60934 | 60 mi = 96.56 km | km → mi × 0.62137 |
| kg → lbs | × 2.20462 | 70 kg = 154.32 lbs | lbs → kg × 0.45359 |
| °C → °F | × 9/5 + 32 | 25°C = 77°F | (°F − 32) × 5/9 |
| Liters → US gal | × 0.26417 | 20 L = 5.28 gal | gal → L × 3.78541 |
| sq m → sq ft | × 10.7639 | 20 m² = 215.28 ft² | ft² → m² × 0.092903 |
| mph → km/h | × 1.60934 | 60 mph = 96.56 km/h | km/h → mph × 0.62137 |
| Meters → feet | × 3.28084 | 5 m = 16.40 ft | ft → m × 0.3048 |
| Hectares → acres | × 2.47105 | 1 ha = 2.47 acres | acres → ha × 0.40469 |
| PSI → bar | × 0.068948 | 30 PSI = 2.07 bar | bar → PSI × 14.5038 |
| °C → Kelvin | + 273.15 | 25°C = 298.15 K | K − 273.15 |
🚀 The NASA $125M Mistake — Why Conversions Matter
In 1999, NASA's Mars Climate Orbiter was destroyed because one engineering team used metric units (newtons) and another used imperial (pound-force). The mismatch sent the spacecraft off course and burned it up in the Martian atmosphere — accurate unit conversion isn't just academic, it's mission-critical.
📐 Metric vs Imperial
The metric system (SI) is decimal-based — all units scale by powers of 10 (1 km = 1,000 m = 100,000 cm). This makes mental arithmetic simple and is used by 195+ countries for science, trade, and everyday life.
The US customary system uses non-decimal scaling (12 inches per foot, 3 feet per yard, 1,760 yards per mile). The US remains one of only three countries (with Myanmar and Liberia) not officially using the metric system.
🌡️ Temperature Scales Explained
Celsius (°C): Water freezes at 0°C, boils at 100°C. Used everywhere except the US for everyday temperature.
Fahrenheit (°F): Water freezes at 32°F, boils at 212°F. Used in the US for weather and cooking.
Kelvin (K): Starts at absolute zero (−273.15°C). No negative values. Used in science and engineering — the only scale where "twice as hot" has true physical meaning.
How Unit Conversion Works
Unit conversion is the process of expressing a measurement in a different unit of the same physical quantity. All conversions within a category use a fixed mathematical relationship — either a multiplication factor (for most units) or a formula for temperature scales, which have different zero points.
Multiplicative Conversions (Most Units)
For length, weight, volume, area, speed, and time, conversion is a simple multiplication. Every unit can be expressed as a fixed ratio to a base unit (the SI base unit for most categories), so converting from unit A to unit B is: multiply by (A's SI factor ÷ B's SI factor).
Example: meters to feet — 1 meter (SI base for length) = 3.28084 feet, so: value_ft = value_m × 3.28084. Area conversions square the linear factor: 1 m² = 10.7639 ft² (3.28084²).Temperature Conversions (Formula-Based)
Temperature scales have different zero points, so a simple multiplication factor doesn't work. Each conversion requires a two-step formula.
Celsius → Fahrenheit: °F = (°C × 9/5) + 32 | Fahrenheit → Celsius: °C = (°F − 32) × 5/9 | Celsius → Kelvin: K = °C + 273.15 | Key reference points: Absolute zero: −273.15°C = −459.67°F = 0 K. Water freezes: 0°C = 32°F = 273.15 K. Body temperature: 37°C = 98.6°F = 310.15 K. Water boils: 100°C = 212°F = 373.15 K.Common Conversion Categories — Reference Guide
Length & Distance — The meter is the most commonly converted measurement. The SI base unit is the meter. Common conversions include meters ↔ feet (factor 3.28084), miles (factor 1.60934), and centimeters ↔ inches (factor 0.393701). The inch was officially defined as exactly 25.4mm in 1959, making all US customary length conversions exact.
Weight & Mass — The SI unit is the kilogram. 1 kg = 20.462 lbs. Note: technically "weight" in physics means force (newtons) while "mass" means the amount of matter (kilograms). In everyday use, weight and mass are interchangeable at Earth's surface. A US ton = 2,000 lbs; a metric tonne = 1,000 kg ≈ 2,204.6 lbs; a UK long ton = 2,240 lbs.
Volume — The SI unit is the cubic meter (m³). Liters (L) is 1/1000 of a cubic meter. US gallon = 3.785411 L, technically imperial gallon = 4.546090 L — a ~20% difference that causes confusion in fuel calculations. US fluid ounce ≈ 29.5735 mL; UK fluid ounce ≈ 28.4131 mL.
Pressure — The SI unit is the pascal (Pa). Common units include bar (100,000 Pa), PSI (pound per square inch, 6,894.76 Pa), and standard atmosphere (atm, 101,325 Pa). Tire pressure in the US is typically 30–35 PSI (2.07–2.41 bar). Standard atmospheric pressure at sea level is 1 atm ≈ 1.01325 bar.
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