Unit Converter
Instantly convert between units of length, mass, temperature, energy, speed, area and volume.
The unit converter lets you instantly transform values between the most widely used measurement systems: the International System (SI), the imperial system and other commonly used units. The categories covered are length, mass, temperature, energy, speed, area and volume, covering the most frequent conversions in science, engineering and everyday life.
For each category, select the source unit and target unit, enter the value and you will get the result instantly. A quick reference table is also shown with equivalent values for 1, 10, 100 and 1,000 units. The converter uses standardised conversion factors or scientific consensus values.
Quick conversion table
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About this converter
This converter performs instant conversions between the most common units of the International System (SI) and other measurement systems. Conversions use exact factors where standardised (e.g. 1 inch = exactly 0.0254 m) or scientific consensus values otherwise.
Source: International System of Units (SI) — BIPM
How conversions work
Converting units means multiplying the original value by a factor that relates both units to a common reference. Internally, the converter first transforms the value into that category's International System base unit (metres for length, kilograms for mass, joules for energy) and then converts it to the target unit. This two-step method ensures that all conversions within the same category are consistent with one another and avoids accumulating rounding errors.
Most common conversions
| Unit | Equals |
|---|---|
| 1 inch | 2.54 cm |
| 1 foot | 30.48 cm |
| 1 mile | 1.609 km |
| 1 pound | 0.454 kg |
| 1 ounce | 28.35 g |
| 1 US gallon | 3.785 L |
| 0 °C | 32 °F |
| 100 °C | 212 °F |
| 1 kcal | 4.184 kJ |
Conversion factors are internationally established. Reference: the International System of Units (SI), defined by the International Bureau of Weights and Measures (BIPM). For high-precision engineering or scientific applications, consult the official normative sources.
Three conversions solved step by step
Converting 90 km/h to metres per second: a kilometre is 1,000 metres and an hour 3,600 seconds, so you simply divide by 3.6. The result is 25 m/s. That constant, 3.6, is worth memorising, because it appears in any kinematics problem. Converting 6 inches to centimetres: an inch is exactly 2.54 cm by international definition, so 6 × 2.54 = 15.24 cm. It is an exact equivalence, not an approximation, since the 1959 yard and pound agreement. Converting 350 °F to Celsius, the typical oven temperature in an American recipe: first subtract 32, then divide by 1.8, that is (350 − 32) / 1.8 = 176.7 °C, which in practice means setting the oven to 175-180 °C. The order of operations matters: dividing first and subtracting afterwards gives the wrong answer.
The mistakes people repeat when converting
The first is treating temperature as a proportional scale. Doubling degrees Celsius does not double the heat, because that scale's zero is conventional, not absolute; this is why conversions with °C and °F involve an addition or subtraction as well as a factor. The second is confusing mass and weight: the kilogram measures mass and the newton measures force, and although everyday language treats them as synonyms, physics does not. The third is assuming a gallon is a gallon: the US one is about 3.785 litres and the British imperial one about 4.546, a twenty per cent difference that ruins any recipe or fuel calculation. The fourth is carrying intermediate rounding: round only at the end, because chaining three conversions and rounding at each step can shift the result appreciably.
Frequently asked questions
Related calculator: Pythagorean theorem