Unit Converter
Convert between hundreds of units across length, weight, temperature, data, energy, and more — all in real time.
1 km is 0.62137119 mi. Both measure length.
Show your working
The same amount in other units
| Length | Equivalent | |
|---|---|---|
| Kilometer | 1 km | your unit |
| Meter | 1,000 m | |
| Decimeter | 10,000 dm | |
| Centimeter | 100,000 cm | |
| Millimeter | 1,000,000 mm | |
| Micrometer | 1,000,000,000 μm | |
| Nanometer | 1,000,000,000,000 nm | |
| Picometer | 1.00000e+15 pm |
Every row is the amount you entered, expressed in that unit.
Assumptions
- Conversions use the internationally agreed definitions of each unit.
- Results are rounded for display; the underlying calculation keeps full precision.
- Ratio units convert by a single fixed factor, so the relationship holds at any size.
- US and imperial units of the same name can differ — gallons and fluid ounces especially.
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Conversion facts
- How many miles is a kilometre?
- One kilometre is 0.621371 miles, so 5 km is 3.106856 miles.
- Why is temperature not a simple multiplication?
- Because the scales have different zero points. 20°C is 68°F, but 0°C is 32°F — the offset matters as much as the ratio.
- Are US and imperial units the same?
- Not always. A US gallon is about 3.785 litres and an imperial gallon about 4.546, so the same word means different amounts.
- How precise are these conversions?
- They use the internationally agreed definitions. Results are rounded for display while the calculation keeps full precision.
How the Converter Works
Select a category from the grid above, enter a value in either field, and the result updates instantly. You can type in either the top or bottom field — both directions work. Click the ⇄ button to swap the two units.
All standard conversions use exact multiplication by a constant factor relative to a base unit (e.g., all lengths relative to the meter). Temperature uses a two-step formula through Kelvin. Fuel efficiency uses km/L as an intermediate. Number base conversion uses JavaScript's built-in integer parsing — for a dedicated binary, octal, and hex tool, try the base converter.
Common Use Cases
- Travel & Navigation: Convert kilometers to miles, km/h to mph, or check fuel economy in your destination country's units.
- Cooking & Recipes: Convert US cups to milliliters, tablespoons to teaspoons, or pounds to grams for international recipes — or use the fractions calculator for fractional cup and spoon quantities.
- Science & Engineering: Work between SI units and imperial units for pressure, energy, power, and torque calculations.
- Computing: Convert between gigabytes, gibibytes, megabytes, and bits for storage calculations. Convert decimal to hex or binary for programming.
- Fitness & Health: Convert pounds to kilograms, inches to centimeters, or calories to kilojoules for nutrition tracking. The BMR calculator applies these conversions to daily calorie needs.
Worked Example
Speed: 100 km/h = 62.1 mph. Weight: 12 stone 4 lb = 78.0 kg. Running pace: 5 min/km = 8:03 min/mile. Recipe: 2.5 US cups = 591 ml. Temperature: 37°C (body temperature) = 98.6°F. Enter any value in either field — the converter updates instantly; click ⇄ to swap the direction.
Accuracy & Data
Conversion factors are based on exact international definitions where they exist (e.g., 1 inch = 0.0254 m exactly; 1 pound = 0.45359237 kg exactly; 1 nautical mile = 1852 m exactly). Derived factors like miles per gallon to km/L are computed from these exact definitions.
All calculations happen in your browser — nothing is sent to a server. Results are rounded to 8 significant figures for display. For scientific applications requiring more precision, verify results against primary standards.
Metric vs imperial
The metric system (SI) is based on powers of 10 — converting between millimetres, centimetres, and metres requires only moving a decimal point. The imperial system uses arbitrary factors: 12 inches to a foot, 3 feet to a yard, 1,760 yards to a mile. Most countries use metric; the US, Myanmar, and the UK (partially) still use imperial for everyday measurements.
SI unit prefixes
Metric prefixes scale any base unit by powers of 10. Common ones: kilo (×1,000), mega (×1,000,000), giga (×1,000,000,000), centi (÷100), milli (÷1,000), micro (÷1,000,000). A kilogram is 1,000 grams; a millimetre is one-thousandth of a metre. This consistency across all units is the main reason scientists worldwide use SI.
Temperature conversion
Celsius and Fahrenheit have different zero points and scale sizes, so conversion requires both multiplication and addition. The formulas: °F = (°C × 9/5) + 32 and °C = (°F − 32) × 5/9. Useful anchors: 0°C = 32°F (freezing), 100°C = 212°F (boiling), and 37°C ≈ 98.6°F (normal body temperature).
Most common conversions
The conversions people look up most often: 1 mile = 1.609 km, 1 kg = 2.205 lb, 1 stone = 6.35 kg (14 lb), 1 inch = 2.54 cm, 1 US gallon = 3.785 litres, 1 UK gallon = 4.546 litres. Note that US and UK gallons differ — a common source of confusion for Americans reading UK fuel economy figures or visiting US recipe websites.
Evidence & Methodology
How This Page Is Grounded
Method
Converts through a canonical base unit using published SI definitions and exact or stated conventional factors.
Important limitation: Some non-SI units have context-specific definitions; the converter labels the convention it uses.
Primary Sources
- The International System of Units (SI Brochure) International Bureau of Weights and Measures
- SI units National Institute of Standards and Technology
Quality Checks
Factors, temperature offsets and round-trip conversion are checked.
See how sources are selected and corrections are handled in our Editorial & Calculation Methodology, and which automated checks this page has to pass in How We Test.
Frequently Asked Questions
How do I convert between units?
Select a category from the grid, enter a value in either field, and the result updates instantly — both directions work. Click the ⇄ button to swap the two units at any time.
What types of units does this converter support?
The unit converter covers length, weight, temperature, area, volume, speed, pressure, energy, power, cooking measurements, digital storage, fuel efficiency, and number bases. All conversions run in your browser with no sign-up required.
How accurate are the conversion results?
Conversion factors are based on exact international definitions — for example, 1 inch = 0.0254 m exactly and 1 pound = 0.45359237 kg exactly. Results are displayed to 8 significant figures.