Home / Unit Converter Tools / Unit Converter

Unit Converter

Length, weight, temperature, volume, and speed, all in one place.

Supported Categories

Switch between categories using the tabs above the converter, each keeps its own independent set of "from" and "to" units and its own sensible default pairing, so switching from Length to Weight, for instance, doesn't require re-selecting units from scratch each time.

How Conversions Work

For most categories, each unit is converted through a common base unit, for example, every length unit is converted to meters first, then from meters to your target unit, which keeps the math consistent across dozens of possible unit pairs. Temperature is the exception, since Celsius, Fahrenheit, and Kelvin don't share a simple multiplication factor, they use their own conversion formulas instead.

Worked Examples for Common Conversions

A few reference points make the underlying math concrete. 1 meter converts to exactly 3.28084 feet, and 1 mile converts to exactly 1.609344 kilometers, both derived from the internationally standardized definition of the inch (2.54 cm) that the imperial system has used since 1959. 1 kilogram converts to 2.204623 pounds, using the standardized international pound (0.45359237 kg exactly). 1 US gallon converts to 3.785412 liters. For speed, 100 km/h converts to 62.137124 mph, a conversion worth knowing for anyone driving in a country that uses a different speed unit than what their car's speedometer defaults to. And for temperature, 100°C converts to exactly 212°F (boiling point of water at sea level), while 0°C converts to exactly 32°F (freezing point), fixed reference points that make it easy to sanity-check any temperature conversion at a glance.

Kelvin: The Scientific Standard

Kelvin, included alongside Celsius and Fahrenheit in this tool's Temperature category, is the standard temperature unit in physics and chemistry specifically because it starts counting from absolute zero, the theoretical point where all thermal motion stops, rather than from an arbitrary reference like water's freezing point. This makes Kelvin uniquely well-suited for scientific calculations where temperature needs to behave proportionally, doubling the Kelvin value genuinely means doubling the thermal energy in a way that doubling a Celsius or Fahrenheit reading does not, since those scales don't start at zero energy. A Kelvin value is always identical in size to its Celsius equivalent, just offset by exactly 273.15, which is why converting between the two is the simplest of the three temperature conversions this tool performs.

Why Temperature Conversion Works Differently

Length, weight, volume, and speed conversions are all simple multiplication, doubling a length in meters doubles it in feet too, because both scales start counting from the same zero point (no length at all). Temperature scales don't share that property: 0°C isn't the same physical temperature as 0°F or 0 Kelvin, each scale defines its own zero point differently (water's freezing point, a historical brine mixture, and absolute zero, respectively). This is why temperature conversion requires an offset in addition to a scaling factor, converting Fahrenheit to Celsius means first subtracting 32 (to align the zero points) and then scaling by 5/9 (to align the degree size), rather than a single multiplication like every other category in this tool uses.

US Customary vs Imperial vs Metric Units

It's a common misconception that "US units" and "imperial units" are the same thing, they actually diverged from a shared British origin and now differ in several important ways. The clearest example is the gallon: this tool's Volume category uses the US gallon (3.785 liters), while the UK's imperial gallon is meaningfully larger, at roughly 4.546 liters, using the wrong one when following a UK recipe or fuel-economy figure introduces a real, non-trivial error. Weight has a similar trap: a metric tonne (1,000 kg), a US short ton (2,000 lb), and a UK long ton (2,240 lb) are three genuinely different weights that all get casually called "a ton" in everyday speech. The metric system avoids this entire category of confusion by design, every unit within a metric category scales by a consistent power of ten with no regional variants, which is a large part of why it's the standard for scientific and international use.

Real-World Uses for a Unit Converter

A Brief History of the Metric System

The metric system was developed in France in the 1790s during the French Revolution, deliberately designed to replace a chaotic patchwork of regional, often town-specific measurement systems with a single, logical, base-10 standard. Its core idea, that every unit within a category should scale by consistent powers of ten (kilo-, centi-, milli-, and so on), made calculations dramatically simpler than the older systems it replaced, no more converting between arbitrary units like feet and inches with an awkward, non-decimal ratio. The system spread gradually worldwide over the following two centuries and is now the official system of measurement in nearly every country, the United States remains one of the few holdouts still using customary units (feet, pounds, gallons) for everyday purposes, even though US scientific and medical fields largely use metric units internally, which is exactly the kind of everyday cross-system friction a tool like this one exists to smooth over.

Why the Imperial and US Customary Systems Still Persist

Despite the metric system's near-universal official adoption, imperial-derived units remain deeply embedded in everyday US life, road signs in miles, recipes in cups, body weight in pounds, largely because of the practical cost and cultural friction of switching an entire country's infrastructure, education, and habits over to a new system. Even countries that have officially gone metric often retain pockets of imperial usage in specific contexts, aviation altitude is measured in feet worldwide by international convention regardless of a country's official system, and some UK road distances are still marked in miles decades after the UK's broader metric transition. This mixed, inconsistent global landscape is exactly why a flexible converter covering both systems remains genuinely useful rather than a historical curiosity, real-world measurement, in practice, is rarely confined to just one system.

Common Mistakes When Converting Units

Mixing up US and UK gallons or tons. As covered above, these aren't interchangeable, always confirm which regional variant a source is actually using before converting.

Confusing a weight ounce with a fluid ounce. They share a name but measure completely different things, mass versus volume, and use entirely different conversion factors, make sure you're using the correct category for what you're actually measuring.

Applying a multiplication shortcut to temperature. Unlike every other category here, temperature can't be converted with a single multiplication factor, the offset described above is required, a common source of small but confusing errors when converting by hand.

Trusting an over-rounded quick mental estimate for something precise. Rough shortcuts like "double Celsius and add 30 for Fahrenheit" are handy for a quick gut-check, but they drift from the true value the further from the reference point you go, use the actual formula (or this tool) whenever the exact figure genuinely matters.

Frequently Asked Questions

Which gallon does this use, US or UK?

This converter uses the US gallon (3.785 liters). The UK imperial gallon is a different size (about 4.546 liters), so keep that in mind if you're converting for a UK context.

Can I quickly reverse a conversion?

Yes, click the swap icon between the two sides to instantly flip the "from" and "to" units.

Is the ounce here a weight ounce or a fluid ounce?

Both exist, but as separate units in separate categories. "Ounces" under the Weight tab measures mass, while "Fluid Ounces" under the Volume tab measures liquid volume, they aren't interchangeable and use entirely different conversion factors.

How precise are the conversion results?

Results are rounded to 6 decimal places, precise enough for virtually any everyday, cooking, DIY, or general reference use. For engineering or scientific work requiring more exact precision or specific significant-figure handling, use the conversion factors directly in a calculation rather than relying on the rounded display.

Why might this show a slightly different result than another converter?

Small discrepancies between converters usually come down to which underlying conversion factor is used, some tools round intermediate values differently, or use a slightly different official definition for a unit like the mile or gallon. This tool uses internationally standardized conversion factors, so results should match other reputable converters to at least 5-6 significant figures.

Why is a tonne different from a US ton?

A metric tonne (1,000 kg, included in this tool's Weight category) is a different unit from a US short ton (2,000 pounds) or a UK long ton (2,240 pounds). All three are sometimes casually referred to as just "a ton," but they represent three genuinely different weights, worth double-checking which one a source actually means.

Related Tools