Free Temperature Converter Online
Type in any field — Celsius, Fahrenheit, or Kelvin — and all other scales update instantly. Adjustable decimal precision.
Celsius (°C)
Water freezes at 0°C, boils at 100°C
Please enter a valid number
Fahrenheit (°F)
Water freezes at 32°F, boils at 212°F
Please enter a valid number
Kelvin (K)
Absolute zero is 0 K (−273.15°C)
Kelvin cannot be below absolute zero (0 K)
Usage Examples
Click any example to load it into the converter
Celsius
↗
Boiling point of water
100°C = 212°F = 373.15 K
Celsius
↗
Freezing point of water
0°C = 32°F = 273.15 K
Celsius
↗
Normal human body temperature
37°C = 98.6°F = 310.15 K
Fahrenheit
↗
Normal body temperature in Fahrenheit
98.6°F = 37°C = 310.15 K
Kelvin
↗
Absolute zero — the lowest possible temperature
0 K = −273.15°C = −459.67°F
Celsius
↗
Comfortable room temperature
20°C = 68°F = 293.15 K
Key Features
Real-time Conversion
Type in any temperature field and all three scales update instantly.
Adjustable Precision
Control decimal places (0–4) for the exact rounding you need.
Full Range Support
Handles absolute zero to extreme temperatures with proper validation.
Reference Points
Clickable presets for boiling, freezing, body temp, room temp, and absolute zero.
Frequently Asked Questions
General
What is the Temperature Converter?
The Temperature Converter instantly translates values between the three major temperature scales: Celsius (°C), Fahrenheit (°F), and Kelvin (K). Type a temperature in any field and the other two scales update in real time with your selected decimal precision (0-4 places). The tool handles the full range from absolute zero upward.
How to Use This Tool
- Type a temperature value into any of the three fields: Celsius, Fahrenheit, or Kelvin.
- All three scales update instantly as you type, with the precision controlled by the decimal places dropdown.
- Click any example card below the converter to auto-populate all fields with a common reference temperature.
Example
Input:
100 °C
Output:
212 °F / 373.15 K
Details
Why does the Celsius-Fahrenheit formula use 9/5 and +32 instead of a simple ratio?
Because the two scales have both different unit sizes and different zero points. The 9/5 factor converts the Celsius degree size to the smaller Fahrenheit degree size: 1 degree Celsius spans the same temperature interval as 1.8 degrees Fahrenheit. The +32 accounts for the offset between the two zero points: 0°C = 32°F. Mathematically, it is a linear transformation y = mx + b where m = 9/5 and b = 32.
What practical difference does the Kelvin scale make in scientific calculations?
Kelvin enables proportional reasoning that Celsius and Fahrenheit prevent. Doubling a temperature from 10°C to 20°C does NOT double the thermal energy. But doubling 283.15 K to 566.3 K (which is 293.15°C) does roughly double the average kinetic energy, because Kelvin starts at true zero. This is why the ideal gas law (PV = nRT) and Stefan-Boltzmann law use Kelvin.
At what temperature are Celsius and Fahrenheit equal?
At -40 degrees. This is the one temperature where both scales read the same numeric value: -40°C = -40°F. You can solve for it by setting the conversion formula equal to itself: x = (9/5)x + 32. This is useful as a quick mental check for any temperature converter — enter -40 and verify both Celsius and Fahrenheit show the same number.
Why does the Kelvin field reject values below 0?
Kelvin is an absolute scale where 0 K (absolute zero) is the theoretical minimum temperature in the universe — the point at which all atomic motion ceases. It is physically impossible to reach temperatures below 0 K according to the laws of thermodynamics. The converter enforces this constraint by displaying an error if you attempt to enter a negative Kelvin value.
How does the Rankine scale relate to these three scales, and why is it not included?
The Rankine scale (°R) is to Fahrenheit what Kelvin is to Celsius: an absolute scale where 0°R = absolute zero, but each degree is the same size as one Fahrenheit degree. The conversion is °R = °F + 459.67. Rankine is used in some engineering thermodynamics texts but is increasingly rare. This converter focuses on the three most widely used scales: Celsius, Fahrenheit, and Kelvin.