Temperature Converter
Temperature measures how hot or cold something is, reflecting the average kinetic energy of the particles in a substance. Unlike length or weight, temperature scales do not all share the same zero point, so converting between them takes more than multiplying by a single factor.
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People convert temperature constantly. A US recipe lists oven heat in Fahrenheit while a European oven dial shows Celsius, a physics problem expects Kelvin, and a thermodynamics table may use Rankine. This converter handles Celsius (C), Fahrenheit (F), Kelvin (K), and Rankine (R) so you can move between everyday, scientific, and engineering scales accurately.
Temperature Units Explained
Celsius is the everyday metric scale: water freezes at 0 C and boils at 100 C at standard pressure. Fahrenheit is standard for daily use in the United States, where water freezes at 32 F and boils at 212 F. Because that range spans 180 Fahrenheit degrees versus 100 Celsius degrees, one Celsius degree equals exactly 1.8 Fahrenheit degrees. Kelvin is the SI scale used in science; its degrees are the same size as Celsius degrees, but it begins at absolute zero (0 K equals minus 273.15 C), so it never goes negative. Rankine is an absolute scale used in some US engineering work; it also starts at absolute zero but uses Fahrenheit-sized degrees, which makes 0 R equal to minus 459.67 F.
How to Convert Temperature Units
Each scale has its own zero, so you scale and shift rather than multiply by one factor. The core formulas are: F = (C times 9/5) + 32; C = (F minus 32) times 5/9; K = C + 273.15; and R = F + 459.67. Worked example, converting 25 C to Fahrenheit: 25 times 9/5 = 45, then 45 + 32 = 77 F. To reach Kelvin, add 273.15: 25 + 273.15 = 298.15 K. Going the other way, convert 98.6 F to Celsius: 98.6 minus 32 = 66.6, then 66.6 times 5/9 = 37 C, normal body temperature. For Rankine directly from Celsius, use R = (C + 273.15) times 9/5, and note that R = K times 9/5.
Common Uses
- Following recipes and setting ovens across Celsius and Fahrenheit
- Reading weather forecasts when traveling between countries
- Solving physics and chemistry problems that require Kelvin
- Engineering and thermodynamics calculations that use Rankine
- Checking body temperature and medical readings
- Setting HVAC, refrigeration, and thermostat targets
Accuracy Tips
Temperature is not proportional, so never just multiply by a ratio: you must apply the full formula with its offset. Watch the order of operations, especially the minus 32 step when going from Fahrenheit. Kelvin and Rankine cannot be negative because they start at absolute zero. Write Kelvin and Rankine values without the word degree (300 K, not 300 degrees K).
Frequently Asked Questions
How do I convert Celsius to Fahrenheit?
Multiply the Celsius value by 9/5 (1.8) and add 32: F = (C times 9/5) + 32. For example, 20 C becomes 20 times 1.8 = 36, plus 32 = 68 F.
What is normal body temperature in Celsius, Fahrenheit, and Kelvin?
Normal body temperature is about 37 C, which equals 98.6 F and 310.15 K.
What is absolute zero on each scale?
Absolute zero is the coldest possible temperature. It equals 0 K, minus 273.15 C, minus 459.67 F, and 0 R.
Why is Kelvin used in science instead of Celsius?
Kelvin starts at absolute zero and never goes negative, so it works directly in physics and chemistry equations such as the ideal gas law, where temperature must be a positive, absolute quantity. Its degree is the same size as a Celsius degree, so K = C + 273.15.
What is Rankine and how does it relate to Kelvin?
Rankine is an absolute temperature scale used in some US engineering fields. It starts at absolute zero like Kelvin but uses Fahrenheit-sized degrees, so R = K times 9/5 and R = F + 459.67. Water freezes at 491.67 R.