Temperature Converter

Free Online Temperature Converter

This temperature converter instantly converts between the four major temperature scales: Celsius (°C), Fahrenheit (°F), Kelvin (K), and Rankine (°R). It works as a celsius to fahrenheit converter, fahrenheit to celsius calculator, celsius to kelvin converter, and kelvin to fahrenheit converter all in one tool, so you never need to memorize the different offset-and-scale formulas each conversion requires.

Whether you're a student solving thermodynamics or chemistry problems, a traveler checking the weather forecast in an unfamiliar unit, a cook following a recipe or oven temperature from a different country, a scientist or engineer working with Kelvin in lab calculations, or simply curious what a Fahrenheit reading feels like in Celsius, this temperature conversion calculator gives you an instant, accurate result along with a visual diagram and complete step-by-step working.

How to Use This Temperature Conversion Calculator

Using this online temperature converter takes only three quick steps. Enter the numeric value you want to convert, choose the scale you're converting from in the "From" dropdown, and choose the scale you want to convert to in the "To" dropdown — the converted result updates instantly as you type. Use the swap button to instantly reverse the conversion direction, or tap one of the popular conversion shortcuts like °C to °F, °F to °C, or °C to K.

• Type the temperature value you want to convert
• Select the scale you're converting from (Celsius, Fahrenheit, Kelvin, or Rankine)
• Select the scale you want to convert to
• Read the converted temperature and the visual conversion diagram with the Celsius base value

Temperature Conversion Formula

Temperature conversion is different from length, weight, or volume conversion because temperature scales are affine, meaning each scale has both a different starting zero point and a different degree size. So instead of one multiplication factor, converting temperature needs both an addition/subtraction step and a multiplication/division step. This calculator always routes through Celsius as the common base scale, since Celsius conversions to and from the other scales are the most standard reference point.

• 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
• Celsius to Rankine: R = (C + 273.15) × 1.8
• Fahrenheit to Kelvin (combined): first convert F to C, then C to K

Key Reference Points on Each Scale

These fixed reference points are useful for sanity-checking any conversion, since they're the same physical temperature expressed on different scales:

• Water freezes: 0 °C = 32 °F = 273.15 K = 491.67 °R
• Water boils (at sea level): 100 °C = 212 °F = 373.15 K = 671.67 °R
• Absolute zero (coldest possible temperature): −273.15 °C = −459.67 °F = 0 K = 0 °R
• Normal human body temperature: approximately 37 °C = 98.6 °F = 310.15 K
• Room temperature: approximately 20–22 °C = 68–72 °F

Worked Example: Celsius to Fahrenheit

Suppose you want to convert 100 °C, the boiling point of water, into Fahrenheit. Using the formula F = C × 9⁄5 + 32, you calculate 100 × 9⁄5 = 180, then add 32 to get 212 °F. So 100 °C equals exactly 212 °F — exactly what the diagram above shows when you enter 100 in the "From: Celsius" field and select "To: Fahrenheit".

Now try the reverse direction: converting a 98.6 °F body temperature reading into Celsius. Using C = (F − 32) × 5⁄9, subtract 32 from 98.6 to get 66.6, then multiply by 5⁄9 to get 37 °C. This two-step "convert to Celsius, then convert out" method is exactly what powers every conversion this calculator performs, no matter which two temperature scales you choose.

Celsius vs Fahrenheit vs Kelvin vs Rankine

The Celsius scale, used by nearly every country in the world, sets 0° at water's freezing point and 100° at its boiling point, making it intuitive for everyday weather and cooking use. The Fahrenheit scale, still used mainly in the United States, sets a finer degree size, so a 1 °F change is smaller than a 1 °C change, which is why weather forecasts in Fahrenheit often use larger numbers.

Kelvin is the SI base unit for temperature used throughout science and engineering, and it starts at absolute zero — the coldest theoretically possible temperature — so there are no negative Kelvin values. Rankine is an absolute scale like Kelvin but uses Fahrenheit-sized degrees, and it appears mainly in some engineering and thermodynamics contexts in the United States.

Where Temperature Conversion Is Used

Temperature conversion comes up constantly outside the classroom, in situations where readings from two different scales need to be compared or combined:

• Weather and travel, reading forecasts or thermostats in an unfamiliar scale abroad
• Cooking and baking, converting oven temperatures between recipes from different countries
• Science and chemistry, converting lab temperature readings to Kelvin for gas law and thermodynamics calculations
• Healthcare, converting body temperature readings between Celsius and Fahrenheit thermometers
• Engineering and manufacturing, working with process or material temperatures across metric and imperial standards
• Meteorology and climate science, standardizing temperature data recorded on different scales