Convert between units of temperature, length, weight, and volume. Select a category, choose your units, and enter a value.
This is an estimate for informational purposes only. Not financial, medical, or professional advice.
Every unit converter works by routing values through a canonical base unit. For length, that base is the metre; for temperature, the kelvin; for weight, the kilogram; for volume, the litre. Any conversion becomes a two-step process: convert the source value into the base unit, then convert from the base into the target unit.
This approach keeps the conversion table minimal (four base units cover every combination) and ensures that a round-trip conversion (e.g. km → miles → km) loses as little precision as possible.
The International System of Units defines seven base units: the foundation for all physical measurements worldwide.
Unlike length, weight, and volume, temperature conversion is not a simple multiplication. Celsius, Fahrenheit, and Kelvin scales have different zero points (offsets) as well as different step sizes (ratios). Conversion requires both an offset and a scale adjustment.
°C → °F: (°C × 9/5) + 32
°F → °C: (°F − 32) × 5/9
°C → K: °C + 273.15
The Kelvin scale is special: zero Kelvin (absolute zero) is the coldest temperature theoretically possible: the point at which all particle motion stops. At −40°, Celsius and Fahrenheit coincide: the only point where both scales agree.
Reference points
Temperature
Length
Weight
Volume
Every unit this calculator converts between traces back to a base unit with its own origin story. Browse the four below.
Temperature: the kelvin
The kelvin is named after William Thomson, later Lord Kelvin, who proposed an absolute temperature scale in 1848 where zero represents the total absence of thermal energy, a point no ordinary substance can reach. Unlike Celsius or Fahrenheit, the kelvin has no negative values by definition.
Weight and temperature are different physical categories, each routed through their own base unit (the kilogram and the kelvin respectively), and each category exists in its own list of compatible units. There is no conversion factor between mass and temperature, they measure fundamentally different physical properties, so mixing categories (e.g. kilograms to Celsius) is rejected as an invalid input rather than silently producing a meaningless number. The same restriction applies to any pairing across categories, such as length to volume, since no physically meaningful conversion factor exists between them either.
Length, weight, and volume convert with a single multiplication factor because their scales all share a zero point (nothing weighs less than 0 kg, and a length or volume of zero means the same absence of quantity on every scale). Celsius, Fahrenheit, and Kelvin do not share a zero point, 0°C is not the same physical temperature as 0°F or 0 K, so temperature conversion needs both an offset (to align the zero points) and a scale adjustment (to align the step sizes), not multiplication alone. This is also why a negative Celsius reading does not simply become a negative Fahrenheit reading of the same relative size.
Results are rounded to 6 significant figures. That removes floating-point noise from the underlying arithmetic (the kind of tiny representation error that all binary floating-point computation is prone to) while keeping enough precision for everyday use, cooking, DIY, travel, and similar everyday conversions rarely need more than a handful of significant digits. It is not a statement about the accuracy of the real-world quantity you started with; a measurement taken with a rough kitchen scale is no more accurate after conversion than it was before.
Every conversion routes through a base unit (e.g. metres for length) and is rounded to 6 significant figures at each step, so a round-trip conversion (for example, miles to kilometres and back to miles) actually performs two separate roundings rather than one. Converting a value out and then back can accumulate a tiny rounding difference from that two-step process, typically far smaller than the precision anyone would notice in practice, not a bug in the conversion factor itself, and not a sign that either conversion direction is wrong.
Temperature accepts negative values, since sub-zero Celsius and Fahrenheit readings are physically real and commonly encountered (a winter morning, a freezer setting). Length, weight, and volume do not, since a negative length, weight, or volume has no physical meaning to convert, there is no such thing as negative five kilograms of anything. Entering a negative value in one of those categories is treated as an invalid input rather than producing a converted negative result.