Unit Converter

Convert length, weight, temperature, area, volume, and speed in one place. Enter a value, choose the units to convert from and to, and see the result instantly — together with the formula the converter used.

Unit converter

Pick a category, enter a value, and convert between units instantly. Everything runs in your browser.

How the unit converter works

The converter is organized into six tabs: Length, Weight / Mass, Temperature, Area, Volume, and Speed. Each tab works the same way. Type a value, pick the unit you are converting from, pick the unit you are converting to, and the result appears immediately. Press Convert to recalculate, or use the swap button between the two dropdowns to exchange the units.

Every calculation happens in your browser with JavaScript — nothing is uploaded or sent to a server. For most quantities the converter works through a base unit: it first expresses your value in the base unit (meters for length, kilograms for weight, liters for volume, meters per second for speed, square meters for area), then converts from the base unit into the target unit. Temperature is handled separately, because Celsius, Fahrenheit, and Kelvin differ by an offset as well as a scale.

Below the result, the tool shows the formula it used, so you can check the arithmetic yourself. Displayed results are rounded to at most ten decimal places to keep long repeating decimals readable.

Conversion formulas

For length, weight, area, volume, and speed, the converter multiplies your value by a single factor:

result = value × (from-unit in base units ÷ to-unit in base units)

For example, one kilometer is 1,000 meters, so converting 2.5 kilometers to meters gives 2.5 × 1,000 = 2,500 meters. Area and volume units scale with the square and the cube of the length factor: 1 m² = 10,000 cm², and 1 m³ = 1,000,000 cm³.

Temperature conversions use these exact formulas:

  • °F = (°C × 9/5) + 32
  • °C = (°F − 32) × 5/9
  • K = °C + 273.15
  • °C = K − 273.15

Worked examples

1. Length: kilometers to meters. Converting 1 kilometer to meters gives 1 × 1,000 = 1,000 m. The tool shows “1 km = 1000 m” with the formula “1 km = 1000 m”.

2. Temperature: Celsius to Fahrenheit. Converting 0 °C to Fahrenheit: (0 × 9/5) + 32 = 32 °F. The tool shows “0 C = 32 F” with the formula “°F = (°C × 9/5) + 32”.

3. Weight: kilograms to pounds. One pound is defined as 0.45359237 kilograms, so 1 kg = 1 ÷ 0.45359237 = 2.2046226218 lb. The tool shows “1 kg = 2.2046226218 lb” (2.20462 lb rounded to five decimals).

4. Speed: kilometers per hour to miles per hour. One kilometer per hour equals 0.6213711922 miles per hour, so 100 km/h = 100 × 0.6213711922 = 62.1371192237 mph.

5. Area: hectares to square meters. One hectare is 10,000 square meters, so 2.5 ha = 2.5 × 10,000 = 25,000 m².

Common mistakes

  • Treating temperature like an ordinary ratio. Converting °C to °F is not just multiplication — the 32-degree offset matters. Doubling 10 °C does not double the Fahrenheit value: 10 °C = 50 °F, but 20 °C = 68 °F, not 100 °F.
  • Confusing mass and weight units. Kilograms, grams, pounds, and ounces here are everyday units of mass. In physics, weight is a force (measured in newtons) that depends on gravity — this converter does not convert force units.
  • Using the wrong gallon. The converter uses the US liquid gallon (3.785411784 liters). The imperial gallon used in the UK is larger, at 4.54609 liters, so fuel-economy figures do not convert one-to-one between the two systems.
  • Forgetting that area and volume factors are squared and cubed. One square meter is 10,000 square centimeters, not 100; one cubic meter is 1,000,000 cubic centimeters, not 100.
  • Mixing statute and nautical miles. The mile in this converter is the statute mile (1.609344 km). The knot is one nautical mile per hour (1.852 km/h) — a different unit, used in aviation and shipping.

Privacy and accuracy

The unit converter runs entirely in your browser. Your values are never sent to a server, stored, or logged — you can even keep using it offline once the page has loaded.

Conversion factors use standard international definitions (for example, 1 inch = 2.54 cm exactly and 1 pound = 0.45359237 kg exactly). Results are rounded to ten decimal places for display, while the underlying arithmetic uses full floating-point precision. For legal, medical, or engineering work that depends on exact rounding rules, verify against the official standard for your field.

Frequently asked questions

How do I convert kilometers to miles?

Open the Length tab, enter your value, set From to Kilometer (km) and To to Mile (mi). One kilometer equals 0.6213711922 miles, so 5 km converts to 3.1068559612 miles.

Why do I add 32 when converting Celsius to Fahrenheit?

Because the two scales start at different points. Water freezes at 0 °C but at 32 °F, so the formula needs that offset: °F = (°C × 9/5) + 32. The 9/5 handles the different size of each degree; the + 32 lines up the starting points.

What is the difference between mass and weight in this converter?

The Weight / Mass tab converts everyday mass units — milligrams, grams, kilograms, tonnes, ounces, pounds, and stone. Strictly speaking, weight is the force gravity exerts on a mass, but in daily life on Earth the two are used interchangeably, and that is what this tab covers.

Which gallon does the volume converter use?

The US liquid gallon of 3.785411784 liters — the gallon used for fuel and groceries in the United States. If you need the UK imperial gallon (4.54609 liters), convert liters instead and apply that factor by hand.

Can I convert square and cubic units?

Yes. Use the Area tab for square units (square meters, acres, square feet) and the Volume tab for cubic units (cubic meters, liters, gallons). Remember the factor grows with the dimension: 1 m³ equals 1,000,000 cm³.

Is my data sent to a server?

No. The conversion runs in JavaScript in your own browser, so nothing you type ever leaves your device.

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