Temperature Converter
How do you convert between Celsius, Fahrenheit, and Kelvin?
Temperature conversion is one of the most common unit conversions people need. Whether you are cooking with an international recipe, checking weather forecasts while traveling, or working on scientific calculations, understanding how to convert between Celsius, Fahrenheit, and Kelvin is essential. Continue your calculation with the Unit Converter, or check the BMI Calculator.
Celsius to Fahrenheit
To convert Celsius to Fahrenheit, multiply the Celsius value by 9/5 (or 1.8) and then add 32. For example, 100 degrees Celsius equals 212 degrees Fahrenheit. The formula is: F = (C x 9/5) + 32. This is the most commonly needed conversion for everyday use, especially when comparing weather temperatures between countries that use different scales.
Fahrenheit to Celsius
To convert Fahrenheit to Celsius, subtract 32 from the Fahrenheit value and then multiply by 5/9. For example, 72 degrees Fahrenheit equals approximately 22.2 degrees Celsius. The formula is: C = (F - 32) x 5/9. This conversion is frequently used by travelers visiting the United States from countries that use the Celsius scale.
Understanding Kelvin
Kelvin is the base unit of temperature in the International System of Units (SI). It is primarily used in scientific contexts. The Kelvin scale starts at absolute zero, the theoretically coldest possible temperature where all molecular motion ceases. To convert Celsius to Kelvin, simply add 273.15. For example, 0 degrees Celsius equals 273.15 Kelvin. Water boils at 373.15 Kelvin (100 degrees Celsius) and freezes at 273.15 Kelvin (0 degrees Celsius).
Common Temperature Reference Points
Some useful temperature benchmarks to remember: water freezes at 0 degrees Celsius (32 degrees Fahrenheit), room temperature is approximately 20 to 22 degrees Celsius (68 to 72 degrees Fahrenheit), normal human body temperature is about 37 degrees Celsius (98.6 degrees Fahrenheit), and water boils at 100 degrees Celsius (212 degrees Fahrenheit) at standard atmospheric pressure.
What should you check before converting units?
Conversions are simple, but accuracy depends on using the correct unit. Always check whether the value is metric, imperial, digital, or temperature-based before comparing results. For work, study, travel, recipes, or shopping, round only at the end so the final number stays more accurate. If a result will be used for safety, construction, medicine, or finance, confirm it with an official standard or professional source.
When do people typically need this?
This converter is useful for travel, recipes, study, product comparison, engineering notes, online shopping, and daily measurements. It is especially helpful when two sources use different systems, such as metric and imperial units.
How can you apply these results practically?
The Temperature Converter is built for people who want a fast answer without losing context. It keeps the calculation simple, shows the result clearly, and helps you understand what the number means before you use it in a real decision.
Conversion tools help translate values between measurement systems quickly. They are especially useful when comparing products, recipes, travel details, technical values, or international information.
What are the three main temperature scales?
Three temperature scales are in common use worldwide. Understanding the relationship between them is essential for cooking (recipes from different countries), science, weather interpretation, and medical contexts.
- Celsius (°C): The international standard for everyday use in most countries including India. Water freezes at 0°C and boils at 100°C at sea level (1 atm pressure). Developed by Anders Celsius in 1742.
- Fahrenheit (°F): Used primarily in the United States. Water freezes at 32°F and boils at 212°F. Developed by Daniel Fahrenheit in 1724. The scale originated from brine (saltwater) freezing point as 0°F and human body temperature as approximately 96°F (now known to be 98.6°F).
- Kelvin (K): The SI base unit of temperature. Used in science and engineering. Absolute zero (0 K) is the theoretical lowest possible temperature — –273.15°C. Kelvin has no degree symbol: 300 K, not 300°K.
What is the exact formula to convert Celsius to Fahrenheit and back?
Celsius to Fahrenheit: °F = (°C × 9/5) + 32
Fahrenheit to Celsius: °C = (°F – 32) × 5/9
Celsius to Kelvin: K = °C + 273.15
Kelvin to Celsius: °C = K – 273.15
Fahrenheit to Kelvin: K = (°F – 32) × 5/9 + 273.15
Key temperature reference points
- Absolute zero: 0 K = –273.15°C = –459.67°F (theoretical minimum temperature)
- Dry ice (CO₂ sublimation): –78.5°C = –109.3°F
- Water freezing: 0°C = 32°F = 273.15 K
- Room temperature (comfortable): 20–22°C = 68–72°F
- Human body temperature: 37°C = 98.6°F (normal oral; core temp is 37.0–37.5°C)
- High fever: 39.5°C = 103.1°F
- Water boiling (sea level): 100°C = 212°F = 373.15 K
- Baking (moderate oven): 180°C = 356°F (fan-forced 160°C)
- Surface of the Sun: ~5,500°C = ~9,932°F
Quick mental conversion tricks
Celsius to Fahrenheit (approximate): Double the Celsius and add 30. Accurate within 2°F between 0°C and 30°C — enough for everyday weather and cooking estimates.
- 15°C: 15 × 2 + 30 = 60°F (actual: 59°F)
- 25°C: 25 × 2 + 30 = 80°F (actual: 77°F)
- 35°C: 35 × 2 + 30 = 100°F (actual: 95°F)
Fahrenheit to Celsius (approximate): Subtract 30 then divide by 2.
- 70°F: (70 – 30) ÷ 2 = 20°C (actual: 21.1°C)
- 100°F: (100 – 30) ÷ 2 = 35°C (actual: 37.8°C)
Temperature in cooking — Celsius vs Fahrenheit oven guide
- Very low (slow cooking): 120–140°C = 250–275°F
- Low: 150–160°C = 300–325°F
- Moderate: 170–180°C = 340–360°F
- Moderately hot: 190–200°C = 375–400°F
- Hot: 210–220°C = 410–430°F
- Very hot (pizza, bread): 230–250°C = 450–480°F
Frequently asked questions about temperature conversion
Is there a temperature where Celsius and Fahrenheit are the same? Yes — at –40 degrees. –40°C = –40°F. This is the one point where both scales intersect, due to the different intervals between degrees and the different zero points.
Why does India use Celsius but the US uses Fahrenheit? India adopted the metric system (including Celsius) in 1956 as part of metrication aligned with international standards. The US is one of the few countries that did not fully adopt the metric system, retaining Fahrenheit for everyday weather and temperature use alongside metric in science.
What temperature is a fever? In adults, a rectal or core temperature above 38.0°C (100.4°F) is clinically defined as fever. An oral temperature above 37.5°C (99.5°F) or axillary (armpit) above 37.2°C (99°F) is generally considered febrile. High fever (above 39.5°C / 103.1°F) warrants medical attention.
Common temperature reference points
| Reference Point | Celsius (°C) | Fahrenheit (°F) | Kelvin (K) |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Liquid nitrogen | −196 | −320.8 | 77.15 |
| Water freezes (at sea level) | 0 | 32 | 273.15 |
| Room temperature | 20–22 | 68–72 | 293–295 |
| Normal body temperature | 37 | 98.6 | 310.15 |
| Fever threshold | 38 | 100.4 | 311.15 |
| Water boils (at sea level) | 100 | 212 | 373.15 |
| Oven — low heat | 150 | 300 | 423 |
| Oven — medium heat | 180 | 350 | 453 |
| Oven — high heat | 230 | 450 | 503 |
| Iron melts | 1,538 | 2,800 | 1,811 |
Reference: conversion factors and equations
| From | To | Formula |
|---|---|---|
| Celsius | Fahrenheit | °F = (°C × 9/5) + 32 |
| Fahrenheit | Celsius | °C = (°F − 32) × 5/9 |
| Celsius | Kelvin | K = °C + 273.15 |
| Kelvin | Celsius | °C = K − 273.15 |
| Fahrenheit | Kelvin | K = (°F + 459.67) × 5/9 |
Sources & References
Sources: BIPM — The International System of Units (SI), 9th edition, 2019 (Kelvin definition via Boltzmann constant); NIST Special Publication 811 — Guide for SI; ASTM E1-14 Standard Specification for ASTM Liquid-in-Glass Thermometers; Anders Celsius original scale paper (1742); Daniel Gabriel Fahrenheit original scale (1724).