Temperature Converter
Convert between Fahrenheit, Celsius, and Kelvin
How to use this calculator
Converting temperatures with this tool takes just a few seconds and requires no mathematical knowledge. Begin by entering your temperature value in the input field at the top of the calculator. You can enter whole numbers like 72, decimal values like 98.6, or negative values like -40 for temperatures below zero. The calculator accepts any numerical input across the full range of possible temperatures.
Next, select the temperature scale you are converting from by clicking one of the three buttons: degrees Fahrenheit, degrees Celsius, or Kelvin. The selected button will highlight to confirm your choice. If you accidentally select the wrong scale, simply click the correct button to change your selection before converting.
Finally, click the Convert button to see your temperature displayed in all three scales simultaneously. The results appear in a clearly formatted box showing equivalent values across Fahrenheit, Celsius, and Kelvin. Your original input scale appears highlighted in the primary result row for easy reference. The converter handles the full range of temperatures, from absolute zero at minus 459.67 degrees Fahrenheit up to extremely high readings used in scientific and industrial contexts.
Understanding temperature scales
Temperature is a measure of thermal energy, representing how fast molecules are moving within a substance. Humans have developed several different scales to express temperature numerically, each with its own origin story, reference points, and practical applications in different fields and regions of the world.
Fahrenheit: The American Standard
Daniel Gabriel Fahrenheit, a German physicist working in Amsterdam, developed this scale in 1724 while crafting precision thermometers. He set zero degrees at the coldest temperature he could reliably create using a mixture of ice, water, and ammonium chloride salt. He then set 96 degrees at the approximate temperature of the human body, measured under the arm. Through these reference points, the scale places water's freezing point at 32 degrees and boiling point at 212 degrees at standard atmospheric pressure. Today, Fahrenheit remains the primary temperature scale in the United States, the Bahamas, Belize, the Cayman Islands, and Palau for weather reports, cooking, and everyday temperature discussions.
Celsius: The Global Standard
Swedish astronomer Anders Celsius proposed this scale in 1742, originally with 100 degrees as the freezing point and 0 degrees as the boiling point of water. Fellow scientist Carl Linnaeus later inverted this arrangement to the current system where water freezes at 0 degrees and boils at 100 degrees. This elegant design based on water's phase changes makes Celsius intuitive for everyday use. The scale is sometimes called Centigrade, meaning "hundred steps," referring to the 100-degree span between freezing and boiling. Nearly every country in the world now uses Celsius as its primary temperature scale for weather forecasts, medical readings, and general communication.
Kelvin: The Scientific Standard
Lord Kelvin, a British physicist, proposed this absolute temperature scale in 1848. It became the standard unit in the International System of Units used by scientists worldwide. Unlike Celsius and Fahrenheit, Kelvin does not use the word "degrees" because it measures absolute temperature starting from the theoretical point where all thermal motion ceases. Zero Kelvin, known as absolute zero, equals minus 273.15 degrees Celsius or minus 459.67 degrees Fahrenheit. Scientists prefer Kelvin because it has no negative values and directly relates to the kinetic energy of molecules, simplifying calculations in physics, chemistry, astronomy, and engineering.
Rankine: The Engineering Scale
William John Macquorn Rankine, a Scottish engineer, developed this scale in 1859 as an absolute temperature scale using Fahrenheit-sized degrees. Like Kelvin, Rankine starts at absolute zero, but each degree equals one Fahrenheit degree rather than one Celsius degree. Engineers in the United States sometimes use Rankine in thermodynamic calculations, particularly in fields like aerospace and steam power generation where Fahrenheit measurements are standard.
Why Different Scales Persist
The existence of multiple temperature scales reflects both historical development and regional preferences. Fahrenheit gained early adoption in English-speaking countries and remains entrenched in American culture despite global standardization on Celsius. Kelvin serves the specific needs of scientific research where absolute measurements matter. Each scale persists because of cultural familiarity, practical utility in specific applications, or scientific necessity for particular calculations.
Frequently asked questions
How can I convert Fahrenheit to Celsius in my head?
For quick mental math, use this approximation: subtract 30 from the Fahrenheit temperature and divide by 2. For example, to estimate 80 degrees Fahrenheit, subtract 30 to get 50, then divide by 2 to get 25 degrees Celsius. The exact answer is 26.7 degrees Celsius, so this shortcut gives you a close approximation for everyday temperatures. For more precision, remember that each 9 Fahrenheit degrees equals 5 Celsius degrees, and adjust from known reference points like 32 degrees Fahrenheit equals 0 degrees Celsius.
Why does the United States still use Fahrenheit?
The United States adopted Fahrenheit during the colonial period when it was the standard throughout the British Empire. While Britain and most former colonies later switched to Celsius as part of metric system adoption in the twentieth century, the United States retained Fahrenheit for everyday use. The cost of changing millions of thermostats, weather signs, medical equipment, cooking instructions, and retraining public familiarity has prevented any serious conversion effort. Additionally, some Americans argue that Fahrenheit provides more precision for weather reporting since its smaller degrees allow for more granular descriptions without decimals.
What exactly is absolute zero?
Absolute zero represents the lowest possible temperature in the universe, defined as 0 Kelvin, minus 273.15 degrees Celsius, or minus 459.67 degrees Fahrenheit. At this temperature, atoms would theoretically have zero kinetic energy and no thermal motion whatsoever. In practice, absolute zero can never be reached due to quantum mechanical effects and the third law of thermodynamics. Scientists have achieved temperatures within billionths of a degree of absolute zero in laboratory settings, but true absolute zero remains physically impossible to attain.
What is normal body temperature in Fahrenheit and Celsius?
Normal human body temperature averages 98.6 degrees Fahrenheit or 37 degrees Celsius when measured orally. However, individual variations between 97 and 99 degrees Fahrenheit (36.1 to 37.2 degrees Celsius) are considered normal and healthy. Body temperature fluctuates throughout the day, typically lowest in early morning and highest in late afternoon or evening. A temperature above 100.4 degrees Fahrenheit or 38 degrees Celsius generally indicates a fever requiring medical attention.
What is considered room temperature?
Room temperature typically refers to a comfortable indoor temperature range of 68 to 72 degrees Fahrenheit, equivalent to 20 to 22 degrees Celsius. Scientific standards often define room temperature more precisely at 68 degrees Fahrenheit or 20 degrees Celsius for laboratory conditions. In cooking and food safety, room temperature usually means around 70 degrees Fahrenheit or 21 degrees Celsius. Wine serving recommendations for "room temperature" often refer to cooler European standards around 60 to 65 degrees Fahrenheit or 15 to 18 degrees Celsius.
What are common oven temperatures in both scales?
Standard oven temperatures span from low heat around 250 degrees Fahrenheit (120 degrees Celsius) to high heat at 450 degrees Fahrenheit (230 degrees Celsius) or above. Common baking temperatures include 325 degrees Fahrenheit (165 degrees Celsius) for slow baking, 350 degrees Fahrenheit (175 degrees Celsius) for standard baking, 375 degrees Fahrenheit (190 degrees Celsius) for cookies and pastries, 400 degrees Fahrenheit (205 degrees Celsius) for roasting, and 425 to 450 degrees Fahrenheit (220 to 230 degrees Celsius) for high-heat roasting and pizza.
At what temperature are Fahrenheit and Celsius equal?
The Fahrenheit and Celsius scales intersect at exactly minus 40 degrees. At this point, minus 40 degrees Fahrenheit equals precisely minus 40 degrees Celsius. This is the only temperature where both scales show the same numerical value. This intersection occurs because the two scales have different zero points and different degree sizes. You can verify this mathematically: plugging minus 40 into the conversion formula (Fahrenheit minus 32, times 5/9) yields minus 40 Celsius.
What are the freezing and boiling points of water?
Water freezes at 32 degrees Fahrenheit, 0 degrees Celsius, or 273.15 Kelvin at standard atmospheric pressure at sea level. Water boils at 212 degrees Fahrenheit, 100 degrees Celsius, or 373.15 Kelvin under the same conditions. These phase transition points shift at different altitudes due to changes in atmospheric pressure. At high elevations like Denver or Mexico City, water boils at lower temperatures because of reduced air pressure, which is why cooking times and recipes often need adjustment at altitude.
Temperature conversion examples
Cooking Conversions
Converting oven temperatures between scales helps when following international recipes. A British recipe calling for 180 degrees Celsius converts to 356 degrees Fahrenheit, which most American bakers round to 350 degrees. A French recipe at 200 degrees Celsius equals 392 degrees Fahrenheit, typically rounded to 400 degrees. For candy making, the soft ball stage at 235 degrees Fahrenheit equals 113 degrees Celsius, while hard crack stage at 300 degrees Fahrenheit equals 149 degrees Celsius.
Understanding Weather Reports
When traveling internationally, understanding Celsius weather forecasts helps with packing decisions. A forecast of 10 degrees Celsius (50 degrees Fahrenheit) means cool weather requiring a jacket. A temperature of 20 degrees Celsius (68 degrees Fahrenheit) indicates mild, comfortable conditions. Readings of 30 degrees Celsius (86 degrees Fahrenheit) signal hot weather, while 35 degrees Celsius (95 degrees Fahrenheit) represents extreme heat requiring precautions against heat exhaustion.
Checking for Fever
Medical thermometers may display readings in either scale. A reading of 99 degrees Fahrenheit (37.2 degrees Celsius) is slightly elevated but often normal. A temperature of 100.4 degrees Fahrenheit (38 degrees Celsius) indicates a low-grade fever. Readings above 102 degrees Fahrenheit (38.9 degrees Celsius) represent moderate fever, while temperatures exceeding 104 degrees Fahrenheit (40 degrees Celsius) constitute high fever requiring immediate medical attention.
Temperature tips and tricks
Quick Mental Math Shortcuts
Memorize key reference points to estimate conversions quickly. Remember that 0 degrees Celsius equals 32 degrees Fahrenheit, 10 degrees Celsius equals 50 degrees Fahrenheit, 20 degrees Celsius equals 68 degrees Fahrenheit, and 30 degrees Celsius equals 86 degrees Fahrenheit. Each 5 degrees Celsius equals 9 degrees Fahrenheit, so you can interpolate between these benchmarks for quick estimates without a calculator.
Key Reference Points to Remember
Commit these essential temperatures to memory for everyday use. Water freezes at 0 degrees Celsius or 32 degrees Fahrenheit. Normal body temperature is 37 degrees Celsius or 98.6 degrees Fahrenheit. A fever begins at 38 degrees Celsius or 100.4 degrees Fahrenheit. Room temperature hovers around 20 degrees Celsius or 68 degrees Fahrenheit. Water boils at 100 degrees Celsius or 212 degrees Fahrenheit at sea level.
Cooking Temperature Adjustments
When converting oven temperatures, round to the nearest standard setting on your oven dial. Most ovens have 25-degree Fahrenheit increments (325, 350, 375, 400, 425). For baking, a difference of 10 degrees Fahrenheit usually does not significantly affect results. For candy making and other precision cooking, use an accurate thermometer rather than relying on oven settings, as actual oven temperatures often vary from dial readings.
Temperature conversion formulas
Fahrenheit to Celsius:
°C = (°F - 32) × 5/9
Celsius to Fahrenheit:
°F = (°C × 9/5) + 32
Celsius to Kelvin:
K = °C + 273.15
Kelvin to Celsius:
°C = K - 273.15
Fahrenheit to Kelvin:
K = (°F - 32) × 5/9 + 273.15
Kelvin to Fahrenheit:
°F = (K - 273.15) × 9/5 + 32
Common temperature references
- Water freezes: 32°F = 0°C = 273.15 K
- Water boils: 212°F = 100°C = 373.15 K
- Room temperature: 68-72°F = 20-22°C
- Body temperature: 98.6°F = 37°C
- Fever threshold: 100.4°F = 38°C
- Hot summer day: 95°F = 35°C
- Cold winter day: 20°F = -6.7°C
- Absolute zero: -459.67°F = -273.15°C = 0 K
Did you know?
- Absolute zero (minus 459.67°F or minus 273.15°C or 0K) is physically impossible to reach, though scientists have achieved temperatures within billionths of a degree.
- The hottest temperature ever recorded on Earth was 134°F (56.7°C) in Death Valley, California, on July 10, 1913.
- Daniel Fahrenheit originally set 0°F based on the coldest temperature he could create with a mixture of ice, water, and salt.
- The surface of the sun reaches approximately 5,500°C (9,932°F), while its core exceeds 15 million degrees Celsius.
- At minus 40 degrees, Fahrenheit and Celsius scales read exactly the same number, the only point where they intersect.