Temperature Scales
Interactive tools for Celsius, Fahrenheit, and Kelvin conversions.
| Conversion | Formula | Example |
|---|---|---|
| C F | °F = (°C × 9/5) + 32 | 100°C → 212°F (Boiling) |
| F C | °C = (°F - 32) × 5/9 | 32°F → 0°C (Freezing) |
| C K | K = °C + 273.15 | 0°C → 273.15 K |
| K C | °C = K - 273.15 | 0 K → -273.15°C |
Absolute Zero
-459.67 °F
Freezing Point
32 °F
Boiling Point
212 °F
Not Just a Number.
Temperature is more than just how hot or cold you feel. It is a direct measure of the chaos of the universe—the average speed of atoms crashing into each other.
Kinetic Theory
Why does hot coffee burn you?
It's a Microscopic Mosh Pit
The molecules in hot coffee are vibrating and moving furiously. When they touch your tongue, they violently transfer that kinetic energy to your cells. **Temperature IS Speed.**
A Tale of Three Scales
- °FThe Human Scale (1724)Daniel Fahrenheit wanted a scale where 0 was the coldest winter day and 100 was body heat. Great for weather, bad for math.
- °CThe Water Scale (1742)Anders Celsius used water as the standard. 0 is freezing, 100 is boiling. Simple, decimal-based, and used by everyone (except USA).
- KThe Absolute Scale (1848)Lord Kelvin realized "negative" temperature makes no sense if temperature is motion. You cannot move slower than stopped. 0 K is the true bottom.
Absolute Zero (0 K)
At -273.15°C, the chaotic dance of atoms comes to a halt. The gas collapses. Electrical resistance vanishes (superconductivity). It is a state of perfect order.
Frequently Asked Questions
Why is -40 degrees the same in Celsius and Fahrenheit?
It is a mathematical coincidence where the two linear scales intersect. The formula $F = 1.8C + 32$ and $C = (F-32)/1.8$ both yield -40 when you plug in -40. It is the only point where they overlap.
Why do scientists use Kelvin?
Scientists use Kelvin because it is an Absolute Scale. In Celsius, '0 degrees' is arbitrary (water freezing). In Kelvin, '0' is the total absence of energy. This means math works better: 200 K actually has twice the thermal energy of 100 K. 20°C does NOT have twice the energy of 10°C.
What is Absolute Zero?
Absolute Zero (0 K or -273.15°C) is the theoretical limit where all atomic motion stops. Heisenberg's Uncertainty Principle says we can't actually reach it perfect zero, but we have gotten very close (billionths of a degree) in labs.
How was the Fahrenheit scale defined?
Daniel Gabriel Fahrenheit (1724) set 0°F as the temperature of a brine mixture (ice, water, and salt), which was the coldest thing he could make in a lab. He set 32°F as water freezing and roughly 96°F as human body temperature. It is quirky compared to Celsius!
What is the Rankine scale?
Rankine (°R) is to Fahrenheit what Kelvin is to Celsius. It is an absolute scale (0°R = Absolute Zero), but the 'size' of each degree is the same as a Fahrenheit degree. It is used heavily in US aerospace engineering.
Is it possible to have negative Kelvin?
In classical terms, No. You cannot have less than zero motion. However, in weird quantum systems with lasers and magnetic fields, physicists can create a state called 'negative temperature' which is predominantly a statistical quirk and is technically 'hotter' than infinite temperature. But for daily life: No.
Why does the US still use Fahrenheit?
Inertia and cost. Converting the entire US infrastructure (road signs, weather stations, manufacturing specs) to Celsius would cost billions. Also, Fahrenheit is often argued to be better for weather, as 0°F is really cold and 100°F is really hot, covering the typical human experience nicely.
What is the hottest temperature possible?
The theoretical limit is the Planck Temperature ($1.4 imes 10^{32}$ K). Beyond this point, our known laws of physics break down because the energy density is so high that quantum gravity effects take over.
Does wind chill change the actual temperature?
No. A thermometer will read the same temperature regardless of the wind. Wind Chill measures Heat Loss. Wind strips away the warm layer of air next to your skin, making you lose heat faster, so it feels colder, but the air temperature is unchanged.
How do I convert Celsius to Kelvin?
It is simple: just add 273.15. So $K = C + 273.15$. Remember, you generally do not use the degree symbol (°) with Kelvin. It is just 'Kelvin', not 'degrees Kelvin'.