Temperature Converter

Convert Temperatures Online — Celsius, Fahrenheit, and Kelvin

Our free temperature converter lets you instantly switch between Celsius, Fahrenheit, and Kelvin scales. Whether you are checking a weather forecast from another country, adjusting a recipe, or working through a physics problem, this tool delivers accurate results in real time. All calculations run directly in your browser — no data is sent to any server, and no sign-up is required.

How to Convert Between Temperature Scales

Temperature conversion relies on simple linear formulas that relate each scale to the others. Below are the key formulas you need, along with step-by-step examples.

Celsius to Fahrenheit

The formula is °F = (°C × 9/5) + 32. Multiply the Celsius value by 1.8 (which is 9 divided by 5), then add 32. For example, to convert 25°C: 25 × 1.8 = 45, then 45 + 32 = 77°F. Room temperature of 25 degrees Celsius equals 77 degrees Fahrenheit.

Fahrenheit to Celsius

The formula is °C = (°F − 32) × 5/9. Subtract 32 from the Fahrenheit value, then multiply by 0.5556. For example, to convert 98.6°F: 98.6 − 32 = 66.6, then 66.6 × 5/9 = 37°C. Normal human body temperature of 98.6°F equals exactly 37°C.

Celsius to Kelvin

The formula is K = °C + 273.15. Simply add 273.15 to the Celsius value. For example, water boils at 100°C, which equals 373.15 K. The Kelvin scale starts at absolute zero, the lowest theoretically possible temperature.

Kelvin to Celsius

The formula is °C = K − 273.15. Subtract 273.15 from the Kelvin value. For example, 300 K equals 26.85°C, which is a comfortable room temperature.

Fahrenheit to Kelvin

The formula is K = (°F − 32) × 5/9 + 273.15. First convert Fahrenheit to Celsius, then add 273.15. For example, 212°F (boiling water) converts to 100°C, then to 373.15 K.

About the Temperature Converter

Temperature measurement is fundamental to science, cooking, medicine, weather forecasting, and countless industrial processes. Different regions and disciplines prefer different scales, making conversion a daily necessity for millions of people worldwide. This converter supports all three major temperature scales and handles both positive and negative values with full decimal precision.

Understanding Temperature Scales

The Celsius scale, also known as centigrade, was developed by Swedish astronomer Anders Celsius in 1742. It defines 0°C as the freezing point of water and 100°C as the boiling point at standard atmospheric pressure. Most countries around the world use Celsius for everyday temperature measurement, weather reports, and cooking. The scale is part of the metric system and is the standard in scientific research alongside Kelvin.

The Fahrenheit scale was proposed by German physicist Daniel Gabriel Fahrenheit in 1724. It sets the freezing point of water at 32°F and the boiling point at 212°F, creating a 180-degree interval between the two reference points. The United States, along with a few other territories, continues to use Fahrenheit for weather forecasts, cooking temperatures, and general daily use. Many people find Fahrenheit more intuitive for describing outdoor weather because the 0-100 range roughly corresponds to the extremes of habitable temperatures.

The Kelvin scale is the SI base unit of temperature, named after Irish-Scottish physicist Lord Kelvin. It uses the same increment size as Celsius but starts at absolute zero — the point where all molecular motion ceases, equal to −273.15°C or −459.67°F. Scientists and engineers prefer Kelvin because it avoids negative values in thermodynamic calculations. You will encounter Kelvin in physics, chemistry, astronomy, and engineering contexts. Unlike Celsius and Fahrenheit, Kelvin does not use the degree symbol; temperatures are simply written as "300 K" rather than "300°K."

There are also less common temperature scales worth mentioning. The Rankine scale is the Fahrenheit equivalent of Kelvin — it starts at absolute zero but uses Fahrenheit-sized degrees. It is occasionally used in American engineering, particularly in thermodynamic calculations involving the Rankine cycle for steam turbines. The Réaumur scale, which sets water's freezing point at 0 and boiling point at 80 degrees, was once popular in France and Germany but is now largely obsolete except in some European cheese and candy making traditions.

Common Temperature Conversions in Daily Life

Cooking is one of the most frequent reasons people need to convert temperatures. American recipes typically list oven temperatures in Fahrenheit — 350°F for baking, 425°F for roasting — while European and Asian recipes use Celsius. A quick conversion helps avoid undercooked or burnt food. For example, 180°C equals 356°F, which is the standard baking temperature in metric countries.

Medical professionals regularly convert between scales when communicating across borders. Normal body temperature is 37°C or 98.6°F. A fever is generally considered to start at 38°C (100.4°F). Pediatricians, nurses, and travelers benefit from knowing these equivalents by heart. Our Celsius to Fahrenheit converter is especially popular for this use case.

Weather is another common scenario. If you are traveling from the United States to Europe, you will see forecasts in Celsius. Knowing that 30°C means a hot summer day (86°F) or that 0°C means freezing conditions (32°F) helps you pack appropriately. Similarly, scientists working with cryogenic materials or high-temperature industrial processes rely on the Celsius to Kelvin converter for precise calculations.

Tips and Quick Reference

A handy shortcut for rough Celsius to Fahrenheit conversion: double the Celsius value and add 30. This gives an approximate result that works well for everyday temperatures. For instance, 20°C becomes roughly 70°F (actual: 68°F), and 35°C becomes roughly 100°F (actual: 95°F). The approximation is less accurate at extreme temperatures but perfectly useful for quick mental math.

Another useful reference point: −40 is the same in both Celsius and Fahrenheit. This is the only temperature where the two scales intersect. Remembering this fact can help you calibrate your intuition when working with negative temperatures.

For Kelvin conversions, remember that room temperature is approximately 293-298 K, water freezes at 273.15 K, and water boils at 373.15 K. In astronomy, stellar surface temperatures are always expressed in Kelvin — our Sun's surface is about 5,778 K. If you work with other unit types, our free length unit converter and online weight unit converter follow the same instant-conversion approach.

Common Temperature Reference Values

The following reference points are useful for quick lookups and sanity-checking your conversions. These cover the most frequently searched temperature equivalents across cooking, weather, science, and medicine.

Description	Celsius	Fahrenheit	Kelvin
Absolute zero	−273.15°C	−459.67°F	0 K
Water freezes	0°C	32°F	273.15 K
Comfortable room	22°C	71.6°F	295.15 K
Body temperature	37°C	98.6°F	310.15 K
Fever threshold	38°C	100.4°F	311.15 K
Hot summer day	40°C	104°F	313.15 K
Water boils	100°C	212°F	373.15 K
Oven baking	180°C	356°F	453.15 K
Oven roasting	220°C	428°F	493.15 K

Frequently Asked Questions

What is 37 degrees Celsius in Fahrenheit?

37°C equals 98.6°F. This is the standard normal human body temperature. Medical thermometers in the United States display Fahrenheit, while most other countries use Celsius. A reading above 38°C (100.4°F) is generally considered a fever.

Why does the United States still use Fahrenheit?

The United States adopted Fahrenheit before the metric system became widespread. While Congress authorized metric use in 1866 and again in 1975, adoption has been voluntary rather than mandatory. Cultural inertia, the cost of changing infrastructure, and public familiarity with Fahrenheit have kept it as the dominant scale for everyday use. Scientific and military contexts in the US do use Celsius and Kelvin.

What is absolute zero and why does it matter?

Absolute zero is 0 Kelvin, equivalent to −273.15°C or −459.67°F. It represents the theoretical lowest temperature, where particles have minimal vibrational motion. No laboratory has ever reached true absolute zero, though scientists have cooled atoms to within billionths of a degree. Absolute zero is important in thermodynamics, quantum mechanics, and superconductor research.

Is there a temperature where Celsius and Fahrenheit are equal?

Yes. At −40 degrees, Celsius and Fahrenheit give the same reading. You can verify this with the formula: (−40 × 9/5) + 32 = −72 + 32 = −40. This crossover point is a useful fact for mental calibration and is sometimes used as a trick question in science classes.

How accurate is this temperature converter?

This converter uses IEEE 754 double-precision floating-point arithmetic, which provides approximately 15-17 significant decimal digits of precision. For all practical purposes — cooking, weather, medicine, and engineering — the results are exact. The calculations happen entirely in your browser using JavaScript, so there is no rounding from server-side processing or network transmission.

What is the difference between Celsius and centigrade?

They are the same scale. The name "centigrade" was used historically because the scale has 100 degrees between the freezing and boiling points of water. In 1948, the General Conference on Weights and Measures officially renamed it to "Celsius" in honor of Anders Celsius. You may still encounter "centigrade" in older textbooks and some regions, but both terms refer to identical temperature values.

When should I use Kelvin instead of Celsius?

Use Kelvin whenever you are working with thermodynamic equations, gas laws, or any formula that requires an absolute temperature scale. The ideal gas law (PV = nRT), Stefan-Boltzmann law, and Wien's displacement law all require Kelvin. In everyday life, Celsius or Fahrenheit is more practical. Kelvin is also the standard in astronomy for expressing stellar temperatures and cosmic background radiation.

How do I convert oven temperatures between Celsius and Fahrenheit?

Common oven conversions include: 150°C = 302°F (slow oven), 180°C = 356°F (moderate oven), 200°C = 392°F (moderately hot), 220°C = 428°F (hot oven), and 250°C = 482°F (very hot). Gas mark equivalents vary by manufacturer. For precise conversions of any oven temperature, use the converter above or visit our dedicated Fahrenheit to Celsius converter page.

What are some extreme temperatures found in nature?

The coldest naturally recorded temperature on Earth was −89.2°C (−128.6°F) at Vostok Station in Antarctica in 1983. The hottest reliably recorded air temperature was 56.7°C (134°F) in Death Valley, California, in 1913. Beyond Earth, the surface of Venus reaches about 462°C (864°F), while the cosmic microwave background radiation sits at 2.725 K (−270.4°C). The core of our Sun reaches approximately 15 million Kelvin, and the centers of the hottest stars can exceed 100 million Kelvin.

How do I convert negative temperatures?

The same formulas apply to negative values. For example, to convert −20°C to Fahrenheit: (−20 × 9/5) + 32 = −36 + 32 = −4°F. For Kelvin, simply add 273.15: −20 + 273.15 = 253.15 K. Note that Kelvin cannot be negative — if your calculation yields a negative Kelvin value, the input temperature is below absolute zero, which is physically impossible. Our converter handles negative inputs correctly for both Celsius and Fahrenheit.

What temperature is considered a fever?

A body temperature above 38°C (100.4°F) is generally classified as a fever by most medical organizations. Normal body temperature can vary slightly between individuals, typically ranging from 36.1°C to 37.2°C (97°F to 99°F). Factors like time of day, physical activity, and age can influence your baseline temperature. Hypothermia begins when core body temperature drops below 35°C (95°F), which is a medical emergency requiring immediate attention. Hyperthermia, or dangerously high body temperature, occurs above 40°C (104°F) and can lead to heat stroke if untreated.

How do temperature scales affect scientific experiments?

In scientific research, using the wrong temperature scale can lead to catastrophic errors. Chemical reaction rates, material properties, and biological processes are all temperature-dependent. The Arrhenius equation, which describes how reaction rates change with temperature, requires absolute temperature in Kelvin. Using Celsius in such equations would produce meaningless results because the zero point is arbitrary. Similarly, thermal expansion calculations, black-body radiation formulas, and entropy computations all demand Kelvin. Laboratory protocols always specify which scale to use, and researchers must convert carefully when referencing data from different sources or countries.

Can I use this converter offline?

Yes. Because all calculations run in your browser using client-side JavaScript, the converter works without an internet connection once the page has loaded. No data is transmitted to any server during the conversion process. This makes it ideal for use in classrooms, laboratories, kitchens, and field work where internet access may be limited or unreliable. Simply bookmark this page for quick access anytime you need to convert between Celsius, Fahrenheit, and Kelvin temperature scales.