Temperature Measurements Conversion
Online temperature measurements conversion calculator and formulas
Temperature Units Calculator
Temperature Converter
Select the temperature scale that you know and enter its value. The calculator supports SI units, common scales, and historic scales.
Temperature Scales - Overview
SI System
Absolute zero: 0 K = -273.15 °C = -459.67 °F
Water Freezing
0 °C
32 °F
273.15 KWater Boiling
100 °C
212 °F
373.15 KQuick Conversions
- °F = °C × 1.8 + 32
- °C = (°F - 32) × 5/9
- K = °C + 273.15
- °C = K - 273.15
- °Ra = °F + 459.67
Kelvin (K) - SI Unit
The Kelvin is the SI base unit for temperature:
- Absolute temperature scale
- Zero point at absolute zero (-273.15°C)
- Same scale size as Celsius
- Used in science and engineering
- Named after Lord Kelvin (William Thomson)
Celsius (°C)
The Celsius scale is the most common worldwide:
- 0°C = water freezing point
- 100°C = water boiling point (at sea level)
- Derived SI unit
- Used in most countries
- Named after Anders Celsius (1742)
Fahrenheit (°F)
The Fahrenheit scale is used in the USA:
- 32°F = water freezing point
- 212°F = water boiling point
- Scale divided into 180 degrees
- Used in USA, Cayman Islands, Bahamas
- Named after Daniel Gabriel Fahrenheit (1724)
Historic Scales
Historic temperature scales still used occasionally:
- Réaumur (°Ré): 0-80° for water freezing-boiling
- Rankine (°Ra): Absolute scale like Kelvin, Fahrenheit-sized
- Delisle (°De): Inverted scale, 150° at freezing
- Newton (°N): 0-33° for water freezing-boiling
- Rømer (°Rø): 7.5-60° for water freezing-boiling
Absolute Zero
Absolute zero is the lowest possible temperature where particles have minimum thermal motion. It equals 0 K = -273.15 °C = -459.67 °F = 0 °Ra. This is the theoretical limit; it cannot be reached in practice.
Temperature Scales Description
Scales with SI Units
Kelvin (K)
The unit of thermodynamic temperature is the Kelvin with the symbol K. The Kelvin is a basic SI unit. It is the 273.16th part of the thermodynamic temperature of the triple point of water, in which its solid, liquid and gaseous phase coexist. The zero point of the Kelvin scale at absolute zero is −273.15 °C.
- Absolute temperature scale
- 0 K = absolute zero
- 273.15 K = 0 °C (water freezing)
- 373.15 K = 100 °C (water boiling)
Celsius (°C)
According to its modern definition, the Celsius temperature no longer indicates the empirical temperature of the historical Celsius scale, but is the thermodynamic temperature on the Kelvin scale with a numerical value that is 273.15 lower: The unit degree Celsius (°C) is a derived SI unit. The degree Celsius scale is identical to the Kelvin. Temperature differences are given in K; the difference between two Celsius temperatures can also be given in °C. The numerical value is the same in both cases.
\(T_C = T_K - 273.15\)
\(T_K = T_C + 273.15\)
Scales without SI Unit
Fahrenheit & Rankine
In the USA, the Fahrenheit scale with the unit degree Fahrenheit (unit symbol: °F) is still in use. The absolute temperature based on Fahrenheit is denoted by degrees Rankine (unit symbol: °Ra). The Rankine scale has the zero point like the Kelvin scale at absolute temperature zero, in contrast to this, however, the scale intervals of the Fahrenheit scale.
- 32 °F = 0 °C (water freezing)
- 212 °F = 100 °C (water boiling)
- 0 °Ra = absolute zero
- °Ra = °F + 459.67
Historic Scales
Several historic temperature scales were used in the past, each with different reference points:
- Réaumur: 0°Ré (freezing) to 80°Ré (boiling)
- Delisle: Inverted, 150°De (freezing) to 0°De (boiling)
- Newton: 0°N (freezing) to 33°N (boiling)
- Rømer: 7.5°Rø (freezing) to 60°Rø (boiling)
Practical Note
Today, only Celsius, Fahrenheit, and Kelvin are commonly used. Historic scales are rarely encountered except in historical documents or specific scientific contexts.
Formulas for Converting Temperature Units
Convert from Kelvin to
| Celsius | \(T_K − 273.15\) |
| Fahrenheit | \(T_K × 1.8 − 459.67\) |
| Rankine | \(T_K × 1.8\) |
| Réaumur | \((T_K − 273.15) × 0.8\) |
| Delisle | \((373.15 − T_K) × 1.5\) |
| Newton | \((T_K − 273.15) × 0.33\) |
| Rømer | \((T_K − 273.15) × 21⁄40 + 7.5\) |
Convert from Celsius to
| Kelvin | \(T_C + 273.15\) |
| Fahrenheit | \(T_C × 1.8 + 32\) |
| Rankine | \(T_C × 1.8 + 491.67\) |
| Réaumur | \(T_C × 0.8\) |
| Delisle | \((100 − T_C) × 1.5\) |
| Newton | \(T_C × 0.33\) |
| Rømer | \(T_C × 21⁄40 + 7.5\) |
Convert from Fahrenheit to
| Celsius | \((T_F − 32) × 5⁄9\) |
| Kelvin | \((T_F + 459.67) × 5⁄9\) |
| Rankine | \(T_F + 459.67\) |
| Réaumur | \((T_F − 32) × 4⁄9\) |
| Delisle | \((212 − T_F) × 5⁄6\) |
| Newton | \((T_F − 32) × 11⁄60\) |
| Rømer | \((T_F − 32) × 7⁄24 + 7.5\) |
Convert from Rankine to
| Kelvin | \(T_{Ra} × 5⁄9\) |
| Celsius | \(T_{Ra} × 5⁄9 − 273.15\) |
| Fahrenheit | \(T_{Ra} − 459.67\) |
| Réaumur | \(T_{Ra} × 4⁄9 − 218.52\) |
| Delisle | \((671.67 − T_{Ra}) × 5⁄6\) |
| Newton | \((T_{Ra} − 491.67) × 11⁄60\) |
| Rømer | \((T_{Ra} − 491.67) × 7⁄24 + 7.5\) |
Convert from Réaumur to
| Kelvin | \(T_{Ré} × 1.25 + 273.15\) |
| Celsius | \(T_{Ré} × 1.25\) |
| Fahrenheit | \(T_{Ré} × 2.25 + 32\) |
| Rankine | \(T_{Ré} × 2.25 + 491.67\) |
| Delisle | \((80 − T_{Ré}) × 1.875\) |
| Newton | \(T_{Ré} × 33⁄80\) |
| Rømer | \(T_{Ré} × 21⁄32 + 7.5\) |
Convert from Delisle to
| Kelvin | \(373.15 − T_{De} × 2⁄3\) |
| Celsius | \(100 − T_{De} × 2⁄3\) |
| Fahrenheit | \(212 − T_{De} × 1.2\) |
| Rankine | \(671.67 − T_{De} × 1.2\) |
| Réaumur | \(80 − T_{De} × 8⁄15\) |
| Newton | \(33 − T_{De} × 0.22\) |
| Rømer | \(60 − T_{De} × 0.35\) |
Convert from Newton to
| Kelvin | \(T_N × 100⁄33 + 273.15\) |
| Celsius | \(T_N × 100⁄33\) |
| Fahrenheit | \(T_N × 60⁄11 + 32\) |
| Rankine | \(T_N × 60⁄11 + 491.67\) |
| Réaumur | \(T_N × 80⁄33\) |
| Delisle | \((33 − T_N) × 50⁄11\) |
| Rømer | \(T_N × 35⁄22 + 7.5\) |
Convert from Rømer to
| Kelvin | \((T_{Rø} − 7.5) × 40⁄21 + 273.15\) |
| Celsius | \((T_{Rø} − 7.5) × 40⁄21\) |
| Fahrenheit | \((T_{Rø} − 7.5) × 24⁄7 + 32\) |
| Rankine | \((T_{Rø} − 7.5) × 24⁄7 + 491.67\) |
| Réaumur | \((T_{Rø} − 7.5) × 32⁄21\) |
| Delisle | \((60 − T_{Rø}) × 20⁄7\) |
| Newton | \((T_{Rø} − 7.5) × 22⁄35\) |
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