Math & Conversion

Temperature Converter

Instantly convert between all 7 temperature scales — Celsius, Fahrenheit, Kelvin, Rankine, Réaumur, Newton, and Delisle. See every unit at once, with step-by-step formulas, real-life reference points, and a complete temperature science guide.

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Temperature Converter — All 7 Scales Simultaneously Live

Type any temperature in any unit — all other scales update instantly in real-time. Or pick a conversion mode for step-by-step formulas

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Celsius (°C)
Metric standard
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Fahrenheit (°F)
US / Imperial
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Kelvin (K)
Scientific / SI
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Rankine (°R)
Engineering
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Réaumur (°Ré)
Historic / wine
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Newton (°N)
Isaac Newton, 1700
°C
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🌡️ Celsius → All Units — Real-time conversion from Celsius
°F = (°C × 9/5) + 32 · K = °C + 273.15 · °R = (°C + 273.15) × 9/5
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°C
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Converted
All 7 Temperature Scales — Simultaneously
Key Conversions at a Glance
Complete Conversion Table with Formulas
Detailed Results — All Units
Relative Temperature — Visual Comparison
Step-by-Step Conversion Working
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    What Is Temperature? — Complete Science Guide

    Understanding temperature, thermodynamic scales, absolute zero, and why different units exist

    Fundamentals
    Temperature — The Measure of Molecular Motion

    Temperature is a physical quantity that expresses the degree of hotness or coldness of a body. On the molecular level, temperature is a direct measure of the average kinetic energy of the particles in a substance — the faster the particles move and vibrate, the higher the temperature. This definition, rooted in statistical mechanics and thermodynamics, explains why there is a lower limit to temperature (absolute zero) but no theoretical upper limit.

    Temperature is measured using a thermometric scale — a standardised system with defined reference points and equal-interval divisions. All common temperature scales are defined by two fixed reference points: the freezing point of pure water at standard atmospheric pressure (101.325 kPa), and either the boiling point of water or absolute zero. The interval between these points is then divided into equal units called degrees.

    The three scales in everyday use are Celsius (used by most of the world), Fahrenheit (used primarily in the United States), and Kelvin (the SI unit of thermodynamic temperature used in science and engineering). Kelvin is unique in that it is an absolute scale — zero Kelvin represents the complete absence of thermal energy, meaning it has no negative values.

    Temperature vs Heat: Temperature and heat are related but distinct. Temperature is an intensive property — it does not depend on the amount of matter. Heat is an extensive property — the total thermal energy transferred. A small cup of boiling water (100°C) and a large pot of boiling water (100°C) have the same temperature but very different heat content. This distinction is fundamental in thermodynamics and engineering.
    The 7 Temperature Scales Explained
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    Celsius (°C) — The Global Standard

    Developed by Swedish astronomer Anders Celsius in 1742. Originally defined with 0°C at water's boiling point and 100°C at freezing — later inverted by Linnaeus. Today, 0°C = freezing point of water, 100°C = boiling point at sea level. Used as the primary temperature scale in 195 countries. Formally defined since 1954 relative to the Kelvin scale: °C = K − 273.15.

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    Fahrenheit (°F) — The US Standard

    Proposed by German physicist Daniel Gabriel Fahrenheit in 1724. Originally defined with 0°F as the coldest temperature achievable with a salt-ice mixture, and 96°F as body temperature. Modern definition: 32°F = water's freezing point, 212°F = water's boiling point. Used daily in the United States, Bahamas, Cayman Islands, and Palau. The 180° interval between freeze and boil corresponds to 100° in Celsius.

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    Kelvin (K) — The Scientific Standard

    Named after Lord Kelvin (William Thomson), who proposed the absolute temperature scale in 1848. The SI unit of thermodynamic temperature. Kelvin uses the same degree size as Celsius but starts at absolute zero (0 K = −273.15°C). The Kelvin scale has no degree symbol — just "K". Used in all scientific, astrophysical, and engineering calculations. Absolute zero (0 K) is the theoretical minimum temperature where molecular kinetic energy equals zero.

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    Rankine (°R or °Ra) — Engineering Absolute

    Proposed by Scottish engineer William Rankine in 1859. An absolute temperature scale (like Kelvin) but uses Fahrenheit-size degrees. 0°R = absolute zero = −459.67°F. Water freezes at 491.67°R and boils at 671.67°R. Used primarily in thermodynamic engineering in the United States — particularly in aeronautical and combustion engineering where absolute temperature is required in Fahrenheit-unit equations.

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    Réaumur (°Ré) — The Wine Scale

    Proposed by René Antoine Ferchault de Réaumur in 1730. Water freezes at 0°Ré and boils at 80°Ré (the scale is divided into 80 degrees). Historically important in France and Germany, where it was used in food production — particularly in cheese-making, brewing, and jam production. Still occasionally referenced in European food science. Conversion: °C = °Ré × 1.25.

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    Newton (°N) — Isaac Newton's Scale

    Created by Isaac Newton around 1700, published posthumously in 1701. Water freezes at 0°N and the boiling point of water is 33°N. Newton is said to have used linseed oil as his thermometric fluid. Historically significant as one of the first attempts at a systematic temperature scale. Rarely used today outside historical contexts. Conversion: °C = °N × 100/33.

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    Delisle (°De) — The Inverted Scale

    Created by French astronomer Joseph-Nicolas Delisle in 1732. Uniquely, the Delisle scale runs in the opposite direction — higher numbers mean colder temperatures. Water boils at 0°De and freezes at 150°De. Absolute zero is at 559.725°De. Used in Russia until the mid-18th century before being replaced by Celsius. A historical curiosity — the only common scale where temperature decreases as the number increases.

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    Absolute Zero — The Ultimate Lower Limit

    Absolute zero (0 K, −273.15°C, −459.67°F) is the theoretical lower limit of temperature — the point at which all thermal motion of atoms would cease. It is physically unattainable: the third law of thermodynamics states that no finite series of processes can reduce the temperature of a system to absolute zero. The coldest measured object in the universe is a lab-created Bose-Einstein condensate — approximately 100 picokelvin (0.0000000001 K) above absolute zero.

    Complete Temperature Conversion Formulas — All 42 Combinations

    Every formula for converting between all 7 temperature scales, with worked examples

    With 7 temperature scales, there are 42 possible directed conversions (7 × 6). All of them can be derived from a single intermediate conversion through Celsius: any unit → Celsius → any other unit. Below are the key direct formulas grouped by source unit.

    From → ToFormulaExample (100°C / 212°F)
    °C → °F°F = (°C × 9/5) + 32100°C → (100×1.8)+32 = 212°F
    °C → KK = °C + 273.15100°C → 100+273.15 = 373.15 K
    °C → °R°R = (°C + 273.15) × 9/5100°C → 373.15×1.8 = 671.67°R
    °C → °Ré°Ré = °C × 4/5100°C → 100×0.8 = 80°Ré
    °C → °N°N = °C × 33/100100°C → 100×0.33 = 33°N
    °C → °De°De = (100 − °C) × 3/2100°C → (100−100)×1.5 = 0°De
    °F → °C°C = (°F − 32) × 5/9212°F → (212−32)×5/9 = 100°C
    °F → KK = (°F − 32) × 5/9 + 273.15212°F → 373.15 K
    K → °C°C = K − 273.15373.15K → 373.15−273.15 = 100°C
    K → °F°F = (K − 273.15) × 9/5 + 32373.15K → 212°F
    °R → KK = °R × 5/9671.67°R → 671.67×5/9 = 373.15 K
    °R → °C°C = (°R − 491.67) × 5/9671.67°R → 100°C
    °Ré → °C°C = °Ré × 5/480°Ré → 80×1.25 = 100°C
    °N → °C°C = °N × 100/3333°N → 33×100/33 = 100°C
    °De → °C°C = 100 − (°De × 2/3)0°De → 100−0 = 100°C
    The fastest mental shortcut — Celsius ↔ Fahrenheit: To convert °C to °F quickly: double the Celsius value and add 30 (approximate). Example: 25°C → 25×2+30 = 80°F (exact: 77°F). To convert °F to °C: subtract 30 and halve. Example: 80°F → (80−30)÷2 = 25°C. These shortcuts give answers within 2–3°F accuracy for everyday temperatures (0–40°C range).

    Real-Life Temperature Reference — Key Landmarks in All Scales

    Important temperatures in everyday life, science, cooking, medicine, and nature

    Temperature in Science, Cooking, Medicine & the Universe

    From absolute zero to the temperature of the Sun's core — a complete guide to extreme temperatures

    Temperature spans an extraordinary range in the natural and scientific world — from the theoretical coldness of absolute zero to the scorching plasma of stellar cores. Understanding the extremes of the temperature scale illuminates fundamental physics, chemistry, biology, and engineering.

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    Cryogenics — Ultra-Low Temperatures

    Cryogenics studies matter at temperatures below −150°C (123 K). Liquid nitrogen (−196°C / 77 K) is used for food preservation, dermatology, and electronics cooling. Liquid helium (−269°C / 4 K) enables MRI machines and particle accelerators. At temperatures near 0 K, quantum effects dominate: superfluidity, superconductivity, and Bose-Einstein condensates emerge. The coldest natural temperature in the known universe is the Boomerang Nebula at 1 K (−272°C).

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    High-Temperature Science

    Tungsten melts at 3,422°C (6,192°F) — the highest melting point of any pure element. Plasma, the fourth state of matter, forms above ~10,000°C. The surface of the Sun is ~5,500°C (9,932°F); its core reaches 15,000,000°C (27,000,000°F). Nuclear fusion requires temperatures of 100,000,000°C (100 million°C) to occur. The Big Bang's temperature 10⁻⁴³ seconds after inception was approximately 10³² Kelvin.

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    Cooking Temperature Guide

    Temperature is critical in cooking chemistry. Maillard reaction (browning): 140–165°C. Caramelisation: 160–180°C. Bread baking: 190–230°C. Deep frying: 175–190°C. Protein denaturation begins ~60°C — why eggs solidify. Pasteurisation: 72°C for 15 seconds. Safe minimum internal temperatures: poultry 74°C, beef 63°C, fish 63°C. Sugar syrup stages: soft ball 112°C → hard crack 149°C → caramel 170°C.

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    Medical Temperature Reference

    Normal human body temperature: 36.1–37.2°C (97–99°F), with an average of 37°C (98.6°F). Core temperature varies by 0.5°C through the day (lowest at 4 AM, highest at 4 PM). Fever: >38°C (100.4°F). Hyperthermia/heat stroke: >40°C (104°F) — medical emergency. Hypothermia: <35°C (95°F) — life-threatening below 32°C. Clinical thermometers measure in tenths of a degree because small changes are diagnostically significant.

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    Earth's Temperature Extremes

    Hottest recorded air temperature: 56.7°C (134°F) at Furnace Creek, Death Valley, USA (1913). Coldest recorded air temperature: −89.2°C (−128.6°F) at Vostok Station, Antarctica (1983). The global average surface temperature is approximately 15°C (59°F). Earth's core temperature is estimated at 5,100–6,000°C — similar to the Sun's surface. The troposphere temperature drops ~6.5°C per 1,000 m of altitude.

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    Industrial & Materials Temperature

    Iron melts at 1,538°C (2,800°F); steel castings require 1,560–1,600°C. Glass softens at ~700°C. Common industrial processes: steam turbines operate at 500–600°C; gas turbine combustion chambers reach 1,300–1,500°C. Rocket engines: liquid oxygen (LOX) fuel engines reach 3,300°C in the combustion chamber. Portland cement kiln: 1,400–1,500°C. Aluminium smelting: 660°C. The temperature-resistance properties of materials determine their engineering applications.

    Frequently Asked Questions — Temperature Conversion

    Expert answers to the most searched temperature conversion and science questions

    How do you convert Celsius to Fahrenheit?
    The exact formula is: °F = (°C × 9/5) + 32, or equivalently °F = (°C × 1.8) + 32. Examples: 0°C = 32°F (freezing). 100°C = 212°F (boiling). 37°C = 98.6°F (body temperature). 20°C = 68°F (room temperature). −40°C = −40°F (unique crossover point). Quick mental approximation: double the Celsius value and add 30. Example: 25°C ≈ 25×2+30 = 80°F (exact answer is 77°F — the shortcut gives ±3°F accuracy for everyday temperatures).
    How do you convert Fahrenheit to Celsius?
    The exact formula is: °C = (°F − 32) × 5/9, or equivalently °C = (°F − 32) ÷ 1.8. Examples: 32°F = 0°C. 212°F = 100°C. 98.6°F = 37°C. 72°F = 22.2°C (comfortable room temperature). 0°F = −17.8°C. Quick mental approximation: subtract 30 from Fahrenheit then halve the result. Example: 68°F → (68−30)÷2 = 19°C (exact: 20°C). For body temperature: (98.6−32)×5/9 = 66.6×0.556 = 37°C.
    How do you convert Celsius to Kelvin?
    The formula is: K = °C + 273.15. This is the simplest conversion because the Kelvin and Celsius scales use the same degree size — Kelvin just starts at absolute zero instead of water's freezing point. Examples: 0°C = 273.15 K. 100°C = 373.15 K. 37°C (body temp) = 310.15 K. −273.15°C = 0 K (absolute zero). To convert back: °C = K − 273.15. The 273.15 offset arises from the definition of the triple point of water (0.01°C = 273.16 K), which anchors both scales.
    What temperature is the same in Celsius and Fahrenheit?
    The two scales intersect at exactly −40°. That is: −40°C = −40°F. Proof: using the formula °F = (°C × 1.8) + 32, substituting °C = −40: °F = (−40 × 1.8) + 32 = −72 + 32 = −40°F. ✓ This is the only temperature where both scales give the same numerical reading. It is practically relevant in cold climate engineering, where specifications must work for both Celsius and Fahrenheit countries — writing "−40°" is unambiguous in either system.
    What is absolute zero and can it be reached?
    Absolute zero is 0 K = −273.15°C = −459.67°F — the theoretical temperature at which all thermal motion of atoms ceases completely. It cannot be reached in practice: the Third Law of Thermodynamics states that no finite number of cooling steps can bring a system to absolute zero. Each step gets you closer but can never complete the journey. The coldest temperatures ever achieved in a laboratory are around 10–100 picokelvin (10⁻¹¹ K) — roughly 38 trillionths of a degree above absolute zero — achieved with laser cooling and magnetic trapping techniques. The coldest natural object in the known universe is the Boomerang Nebula at approximately 1 K.
    Why does the US use Fahrenheit instead of Celsius?
    The United States adopted Fahrenheit in the early 1700s when it was introduced by Daniel Fahrenheit, and never switched when the rest of the world moved to Celsius in the 18th and 19th centuries. Fahrenheit was the dominant European scale when the colonies were established. The US attempted metrication in the 1970s (Metric Conversion Act 1975) but it was voluntary and largely failed. Today only the US, Myanmar, and Liberia use Fahrenheit for daily weather. Interestingly, Fahrenheit has advantages for weather: the range 0–100°F maps well to human experience of "very cold" to "very hot" daily temperatures, giving more granularity for distinguishing comfortable temperatures without decimals.
    What is the difference between Kelvin and Rankine?
    Both Kelvin and Rankine are absolute temperature scales starting at absolute zero — they never have negative values. The key difference is degree size: Kelvin uses Celsius-sized degrees (1 K = 1°C change), while Rankine uses Fahrenheit-sized degrees (1°R = 1°F change). Conversion: K = °R × 5/9, or °R = K × 9/5. At absolute zero: 0 K = 0°R. At water's freezing point: 273.15 K = 491.67°R. At water's boiling point: 373.15 K = 671.67°R. Rankine is used in US aerospace and combustion engineering where Fahrenheit units are required in thermodynamic equations (like the ideal gas law: PV = nRT).
    What is normal body temperature in Fahrenheit and Celsius?
    Normal human core body temperature is 37°C (98.6°F), but this is an average — the healthy range is approximately 36.1–37.2°C (97–99°F). Body temperature varies by about 0.5°C throughout the day (lowest around 4 AM, highest around 4–6 PM). Temperature also varies by measurement site: rectal temperature runs ~0.3–0.5°C higher than oral; axillary (armpit) runs ~0.5°C lower. A fever is defined as oral temperature >38°C (100.4°F). The historical 98.6°F figure comes from a 19th-century German study; modern data suggests the average may be slightly lower at ~36.6°C (97.9°F) due to reduced chronic infections in modern populations.
    What is the boiling point and freezing point of water in different temperature scales?
    Water's freezing point (at standard atmospheric pressure): 0°C = 32°F = 273.15 K = 491.67°R = 0°Ré = 0°N = 150°De. Water's boiling point (at 1 atm, 101.325 kPa): 100°C = 212°F = 373.15 K = 671.67°R = 80°Ré = 33°N = 0°De. Note that the Delisle scale is inverted — higher numbers are colder. Also note that water's boiling point decreases with altitude (lower atmospheric pressure): at 2,000 m elevation, water boils at ~93°C (199°F); at the top of Mount Everest (~8,849 m), water boils at approximately 70°C (158°F) — which is why cooking takes longer at high altitude.