Temperature Converters
Every temperature scale in one place — 16 units, 240 conversions, from Celsius, Fahrenheit, and kelvin to the historical Réaumur, Rømer, Delisle, and Newton scales, plus the scientific units physicists actually use. Temperature is the one quantity where you can't just multiply — most scales need an offset formula like °F = °C × 9/5 + 32, and every page here shows the exact one.
Popular temperature converters
The 36 most-searched temperature pairs. Tap any pair to open its dedicated converter with the exact formula, worked examples, and a reference-temperature table.
Conversion matrix
The 10 most-used temperature units, every pair as a clickable link.
The temperature scales compared
Every classic scale is fixed by where it puts absolute zero, the freezing point of water, and the boiling point of water. The Delisle scale famously runs backwards — its numbers fall as temperature rises.
| Scale | Symbol | Absolute zero | Water freezes | Body temp. | Water boils | Degree size (K) |
|---|---|---|---|---|---|---|
| Celsius | °C | -273.15 | 0 | 37 | 100 | 1 |
| Fahrenheit | °F | -459.67 | 32 | 98.6 | 212 | 0.5555555556 |
| Kelvin | K | 0 | 273.15 | 310.15 | 373.15 | 1 |
| Rankine | °R | 0 | 491.67 | 558.27 | 671.67 | 0.5555555556 |
| Réaumur | °Ré | -218.52 | 0 | 29.6 | 80 | 1.25 |
| Rømer | °Rø | -135.90375 | 7.5 | 26.925 | 60 | 1.9047619048 |
| Delisle | °De | 559.725 | 150 | 94.5 | 0 | 0.6666666667 (reversed) |
| Newton | °N | -90.1395 | 0 | 12.21 | 33 | 3.0303030303 |
About temperature measurement
Temperature measures the average kinetic energy of the particles in a substance — how vigorously its atoms and molecules jiggle. In the International System of Units the base unit is the kelvin (K), since 2019 defined by fixing the Boltzmann constant at exactly 1.380649×10⁻²³ joules per kelvin. The kelvin scale starts at absolute zero (0 K = −273.15 °C = −459.67 °F), the floor of thermodynamic temperature where particle motion reaches its quantum minimum — which is why a temperature can never be "below absolute zero," and why our calculators flag any input that would be.
The story of the modern scales is a fifty-year relay across Europe: Ole Rømer in Copenhagen built the first two-fixed-point scale in 1701, the same year Isaac Newton published his linseed-oil scale in London; Daniel Fahrenheit visited Rømer in 1708 and refined the idea with his mercury thermometer in 1724; Réaumur answered from Paris in 1730 with his 80-degree scale, and Delisle built his famously inverted scale in St. Petersburg in 1732. Anders Celsius closed the chapter in 1742 with the 100-degree scale the world now uses, and a century later William Thomson, Lord Kelvin (1848), and W. J. M. Rankine (1859) anchored the Celsius- and Fahrenheit-sized degrees to absolute zero.
Unlike length or weight, temperature conversion is affine, not multiplicative: because the scales place their zeros at different physical points, you must multiply and shift (°F = °C × 9/5 + 32), and the scales even cross — Celsius and Fahrenheit read the same number at −40°. In daily Indian life both systems coexist: weather reports and cooking use Celsius, while fever readings are still commonly quoted in Fahrenheit ("a 102-degree fever" is 38.9 °C). At the extremes, science needs the prefixed kelvins and natural units in our directory: quantum computers run near 15 millikelvin, Bose–Einstein condensates form at nanokelvins, the Sun's core burns at 15.7 megakelvin, fusion plasmas are quoted in kiloelectronvolts, and the Planck temperature (1.4×10³² K) marks where known physics ends.
All temperature units
Tap any unit to expand its full list of outgoing conversions. Units are grouped by family.
Modern Standard Scales
Celsius (°C) — 15 conversions
Fahrenheit (°F) — 15 conversions
Kelvin (K) — 15 conversions
Rankine (°R) — 15 conversions
Historical Scales
Delisle (°De) — 15 conversions
Newton (°N) — 15 conversions
Réaumur (°Ré) — 15 conversions
Rømer (°Rø) — 15 conversions
Scientific & Fixed-Point
Electronvolt (eV) — 15 conversions
Planck Temperature (T_P) — 15 conversions
Triple Point of Water (TPW) — 15 conversions
SI Prefixed Kelvin
Gigakelvin (GK) — 15 conversions
Megakelvin (MK) — 15 conversions
Microkelvin (µK) — 15 conversions
Millikelvin (mK) — 15 conversions
Nanokelvin (nK) — 15 conversions
Frequently asked questions
What is the formula for Celsius to Fahrenheit?
°F = (°C × 9/5) + 32. Multiply the Celsius value by 9/5 (that is, 1.8), then add 32. To go back: °C = (°F − 32) × 5/9. Example: 37 °C × 9/5 + 32 = 98.6 °F, normal body temperature.
Why can't I just multiply when converting temperatures?
Because most temperature scales place their zero points at different physical temperatures. Converting between them needs both a scaling step and an offset — an affine formula, y = Ax + B — not a single ratio. Only conversions between absolute scales that share the same zero (kelvin, Rankine, and the prefixed kelvins) reduce to pure multiplication.
What is absolute zero?
Absolute zero is the lowest possible temperature, where particle motion reaches its quantum-mechanical minimum: exactly 0 K = −273.15 °C = −459.67 °F = 0 °R. No physical system can be cooled below it, which is why every calculator on this site flags readings that would fall under 0 K.
At what temperature are Celsius and Fahrenheit equal?
At −40°. Setting °F = °C in the conversion formula gives x = 1.8x + 32, which solves to x = −40, so −40 °C = −40 °F exactly. It is the only temperature where the two scales read the same number.
What is a normal body temperature in Celsius and Fahrenheit?
About 37 °C, which is exactly 98.6 °F (and 310.15 K). Clinically, anything from roughly 36.1 to 37.2 °C (97 to 99 °F) is considered normal; a reading of 100.4 °F (38 °C) or higher is generally treated as a fever.
Is it "degrees kelvin" or just "kelvins"?
Just kelvins. Since 1967–68 the SI unit has been the kelvin (symbol K, no degree sign): water boils at 373.15 K, not 373.15 °K. Celsius and Fahrenheit, by contrast, keep the degree sign and the word "degrees."
Source & reference
Definitions and conversion relationships on this page follow the BIPM — International System of Units (kelvin defined via the Boltzmann constant, 2019), the International Temperature Scale of 1990 (ITS-90), the NIST guide to the SI, and CODATA recommended values for the fundamental constants. Historical scale definitions (Réaumur, Rømer, Delisle, Newton) follow standard reference works in the history of thermometry.