How do I convert Celsius to Fahrenheit?

To convert Celsius to Fahrenheit, multiply the Celsius temperature by 9/5 and then add 32. The formula is: °F = (°C × 9/5) + 32. For example, 100°C = (100 × 9/5) + 32 = 180 + 32 = 212°F (boiling point of water).

How do I convert Fahrenheit to Celsius?

To convert Fahrenheit to Celsius, subtract 32 from the Fahrenheit value, then multiply by 5/9. The formula is: °C = (°F − 32) × 5/9. For example, 98.6°F = (98.6 − 32) × 5/9 = 66.6 × 5/9 = 37°C (normal body temperature).

What is absolute zero?

Absolute zero is the lowest theoretically possible temperature, at which all molecular motion stops. It is defined as 0 Kelvin (K), which equals −273.15°C or −459.67°F. Nothing in the observable universe can reach absolute zero, though scientists have cooled atoms to within billionths of a degree above it.

Why does Kelvin have no degree symbol?

Kelvin (K) has no degree symbol because it is an absolute thermodynamic scale — not a relative scale like Celsius or Fahrenheit. Since the 1968 International System of Units (SI) revision, the unit is simply called 'kelvin' (lowercase) and its symbol is 'K', not '°K'. The scale starts at absolute zero, making it the SI base unit of thermodynamic temperature.

What is the difference between Celsius and Fahrenheit?

Celsius and Fahrenheit are both relative temperature scales but use different reference points and interval sizes. Celsius sets 0° as water's freezing point and 100° as its boiling point (at sea level), so 1°C = 1/100 of that range. Fahrenheit sets 32° as freezing and 212° as boiling, so 1°F is a smaller increment — about 5/9 of 1°C. The US primarily uses Fahrenheit; most of the world uses Celsius.

What is body temperature in Celsius, Fahrenheit, and Kelvin?

Normal human body temperature is 37°C, 98.6°F, or 310.15 K. This value can vary slightly by individual, time of day, and measurement method. A temperature above 38°C (100.4°F) is generally considered a fever.

What is the Rankine temperature scale?

Rankine (°R) is an absolute temperature scale based on Fahrenheit degrees. Like Kelvin starts at absolute zero using Celsius intervals, Rankine starts at absolute zero (0°R = −459.67°F) using Fahrenheit-sized degrees. It is used in some engineering fields in the United States, particularly in thermodynamics calculations involving Fahrenheit. The conversion is: °R = (°F + 459.67) or K × 9/5.

At what temperature are Celsius and Fahrenheit equal?

Celsius and Fahrenheit are equal at −40 degrees. That is, −40°C = −40°F. You can verify this: °F = (−40 × 9/5) + 32 = −72 + 32 = −40°F. This crossover point is a handy sanity check when working with temperature conversions.

Unit Converter

Temperature Converter

Convert between Celsius, Fahrenheit, Kelvin, Rankine, Newton, Delisle, Réaumur & Rømer — instantly.

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Common Temperature Reference Points

Quick Reference

Reference Point	°C	°F	K	°R
Absolute Zero	−273.15	−459.67	0	0
Water Freezing	0	32	273.15	491.67
Room Temperature	20	68	293.15	527.67
Body Temperature	37	98.6	310.15	558.27
Water Boiling	100	212	373.15	671.67
−40° crossover	−40	−40	233.15	419.67

How It Works — Conversion Formulas

All conversions use Kelvin as the intermediate base. The input is first converted to Kelvin, then from Kelvin to the target scale — eliminating rounding error chains. Below are the direct formulas from Celsius (as reference), since any scale can be converted to Celsius first.

// Formulas from Celsius (°C) to each scale °F = (C × 9/5) + 32 K = C + 273.15 °R = (C + 273.15) × 9/5 °N = C × 33/100 °De = (100 − C) × 3/2 °Ré = C × 4/5 °Rø = (C × 21/40) + 7.5 // Reverse — from Kelvin to each scale (used internally) °C = K − 273.15 °F = K × 9/5 − 459.67 °R = K × 9/5 °N = (K − 273.15) × 33/100 °De = (373.15 − K) × 3/2 °Ré = (K − 273.15) × 4/5 °Rø = (K − 273.15) × 21/40 + 7.5

What is a Temperature Converter?

A temperature converter is a tool that translates a temperature value from one measurement scale to another using established mathematical formulas. Temperature scales differ in their zero points and degree sizes, which means a simple linear factor is not always sufficient — you often need both multiplication and addition (or subtraction). Our converter handles all eight major temperature scales simultaneously, updating every result the moment you type.

Because no external API is involved, conversions happen entirely in your browser and work offline. The calculator routes all conversions through Kelvin as the intermediate step, avoiding accumulated rounding errors when chaining multiple conversions.

Temperature Scales Explained

Eight temperature scales are in active or historical use. Each was developed by different scientists with different reference points in mind:

Scale	Symbol	Freezing Point	Boiling Point	Absolute Zero	Use
Celsius	°C	0	100	−273.15	Worldwide (science & everyday)
Fahrenheit	°F	32	212	−459.67	USA, some Caribbean nations
Kelvin	K	273.15	373.15	0	Science, SI base unit
Rankine	°R	491.67	671.67	0	US engineering/thermodynamics
Newton	°N	0	33	−90.14	Historical (Isaac Newton, 1701)
Delisle	°De	150	0	559.73	Historical (inverted scale)
Réaumur	°Ré	0	80	−218.52	Historical (Europe, dairy)
Rømer	°Rø	7.5	60	−135.9	Historical (Ole Rømer, 1701)

Note: Delisle is an inverted scale — higher values mean colder temperatures.

Common Temperature Conversion Formulas

Celsius ↔ Fahrenheit

°F = (°C × 9/5) + 32
°C = (°F − 32) × 5/9

The most commonly needed conversion. The −40° crossover point is a useful mental check.

Celsius ↔ Kelvin

K = °C + 273.15
°C = K − 273.15

The simplest conversion — just add or subtract 273.15. Same degree size, different zero.

Fahrenheit ↔ Kelvin

K = (°F + 459.67) × 5/9
°F = K × 9/5 − 459.67

Used in thermodynamics calculations when working with US units and SI simultaneously.

Celsius ↔ Rankine

°R = (°C + 273.15) × 9/5
°C = °R × 5/9 − 273.15

Rankine is the absolute-temperature counterpart of Fahrenheit — often used in US aerospace and mechanical engineering.

Temperature in Daily Life

Body Temperature

Normal human body temperature is 37°C (98.6°F / 310.15 K). A fever is typically defined as a body temperature above 38°C (100.4°F). Hypothermia begins when core temperature drops below 35°C (95°F). Medical thermometers are calibrated in Celsius in most countries, Fahrenheit in the USA.

Cooking

Oven temperatures range from 150°C (300°F) for low-and-slow cooking to 250°C (480°F) for high-heat baking. Most recipe websites cater to either Celsius or Fahrenheit readers — a converter is essential when adapting international recipes. Candy-making stages (soft ball, hard crack) have specific temperature windows that must be converted precisely.

Weather

Weather forecasts in the USA use Fahrenheit; almost everywhere else uses Celsius. Key weather thresholds: 0°C (32°F) is the freezing point of water and road ice risk; 35°C (95°F) is extreme heat; −40°C equals −40°F — the only point where both scales agree. Wind chill and heat index values are also reported in the local scale.

Science & Industry

Kelvin is the SI unit for scientific work. Cryogenic applications (liquid nitrogen at −196°C / 77 K) and astrophysics (the cosmic microwave background at 2.7 K) require Kelvin. Chemical reaction rates, semiconductor fabrication, and materials science all specify temperatures in Kelvin. Rankine is used in some US thermodynamic textbooks and aerospace engineering.

Frequently Asked Questions

Multiply the Celsius value by 9/5, then add 32. °F = (°C × 9/5) + 32. For example, 100°C = (100 × 1.8) + 32 = 212°F. A quick mental shortcut: double the Celsius value, subtract 10%, then add 32. That gives you a rough estimate — e.g., 20°C → 40 − 4 + 32 = 68°F.

Subtract 32 from the Fahrenheit value, then multiply by 5/9. °C = (°F − 32) × 5/9. For example, 98.6°F = (98.6 − 32) × 5/9 = 66.6 × 0.5556 = 37°C. Quick estimate: subtract 32, then halve it. That gives you a rough Celsius — useful for weather temperatures.

Absolute zero (0 K = −273.15°C = −459.67°F) is the theoretical temperature at which all molecular kinetic energy reaches its minimum — particles essentially stop moving. It is physically unachievable but approached in laboratory conditions: scientists have cooled atoms to within nanokelvins. It defines the starting point of the Kelvin and Rankine absolute scales, which are essential for thermodynamic equations where negative temperatures would be nonsensical.

Since the 1968 revision of the International System of Units (SI), Kelvin is treated as an absolute thermodynamic quantity, not a relative degree measurement. The symbol is simply "K" — not "°K". The reasoning: a "degree" implies a relative difference from an arbitrary reference point (like water's freezing point), but Kelvin starts at absolute zero, a physically meaningful origin. So you write "310 K" for body temperature, not "310°K".

The two scales intersect at −40°: that is, −40°C = −40°F. You can verify: °F = (−40 × 9/5) + 32 = −72 + 32 = −40°F. This crossover point is a handy sanity check when writing or verifying conversion code. In practical terms, −40° is roughly the temperature of extremely cold Arctic weather and certain industrial freezing processes.

Normal human body temperature (37°C) in all supported scales: 37°C / 98.6°F / 310.15 K / 558.27°R / 12.21°N / 94.5°De / 29.6°Ré / 26.925°Rø. Use the "Body Temp (37°C)" example button at the top of this page to see all values instantly. Note that a fever (38°C) = 100.4°F, and hypothermia begins below 35°C (95°F).

Rankine (°R) is an absolute temperature scale where degree size equals one Fahrenheit degree, but with absolute zero at its origin (0°R = −459.67°F = 0 K). It is primarily used in US engineering fields — particularly in thermodynamics, aerospace, and mechanical engineering textbooks — where working in Fahrenheit-based units is conventional but absolute temperature is required (e.g., in ideal gas law calculations). The conversion is simply: °R = °F + 459.67.

The Newton scale was proposed by Isaac Newton around 1701, setting water's freezing point at 0°N and body temperature at roughly 12°N (boiling water = 33°N). It was one of the earliest calibrated thermometer scales and inspired later work by Celsius and Fahrenheit. The Delisle scale, created by Joseph-Nicolas Delisle in 1732, is unusual because it is inverted — higher values mean colder temperatures. Water boils at 0°De and freezes at 150°De. Both scales are now purely historical and rarely encountered outside of scientific history discussions.