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Convert between Celsius, Fahrenheit, Kelvin, and Rankine instantly. Essential for weather reporting, cooking, scientific research, and engineering calculations.
0 °C
Water Freezes
100 °C
Water Boils
273.15 K
Freezing in Kelvin
-40°
°F = °C Crossover
Key formulas: °C = (°F - 32) × 5/9 | K = °C + 273.15 | °R = °F + 459.67
| Reference Point | Celsius (°C) | Fahrenheit (°F) | Kelvin (K) | Rankine (°R) |
|---|---|---|---|---|
| Absolute Zero | -273.15 | -459.67 | 0 | 0 |
| Liquid Nitrogen | -196 | -320.8 | 77.15 | 138.87 |
| Dry Ice Sublimation | -78.5 | -109.3 | 194.65 | 350.37 |
| F / C Crossover | -40 | -40 | 233.15 | 419.67 |
| Freezing Point of Water | 0 | 32 | 273.15 | 491.67 |
| Cool Room Temperature | 20 | 68 | 293.15 | 527.67 |
| Warm Room Temperature | 25 | 77 | 298.15 | 536.67 |
| Human Body Temperature | 37 | 98.6 | 310.15 | 558.27 |
| Pasteurization Temperature | 72 | 161.6 | 345.15 | 621.27 |
| Boiling Point of Water | 100 | 212 | 373.15 | 671.67 |
| Oven Baking (Moderate) | 177 | 350 | 450.15 | 809.67 |
| Oven Baking (Hot) | 232 | 450 | 505.15 | 909.67 |
| Wood Fire | 600 | 1112 | 873.15 | 1571.67 |
| Iron Melting Point | 1538 | 2800 | 1811.15 | 3260.07 |
| Surface of the Sun | 5505 | 9941 | 5778.15 | 10400.67 |
Temperature is a measure of the average kinetic energy of molecules in a substance. Over the centuries, scientists have developed multiple scales to quantify temperature, each with different reference points and degree sizes. The four scales in common use today are Celsius, Fahrenheit, Kelvin, and Rankine.
Developed by Swedish astronomer Anders Celsius in 1742, Celsius is the most widely used temperature scale globally. It defines the freezing point of water at 0 °C and the boiling point at 100 °C under standard atmospheric pressure. The 100-degree interval between these points makes it intuitive for everyday use. Celsius is the standard in science, medicine, and daily life across most of the world.
Created by Daniel Gabriel Fahrenheit in 1724, this scale sets the freezing point of water at 32 °F and the boiling point at 212 °F. The 180-degree span between these points results in smaller degree increments than Celsius, which some argue provides finer granularity for describing weather temperatures. Fahrenheit remains the standard for everyday use in the United States, its territories, and a few Caribbean nations.
Named after Lord Kelvin (William Thomson), the Kelvin scale is the SI base unit of thermodynamic temperature. It starts at absolute zero (0 K = -273.15 °C), the theoretical point where all molecular motion stops. Each kelvin increment is the same size as one Celsius degree. Because there are no negative values on the Kelvin scale, it is the preferred unit in physics, chemistry, and astronomy. Note that temperatures in kelvin are written without a degree symbol.
Proposed by Scottish engineer William John Macquorn Rankine in 1859, the Rankine scale is an absolute temperature scale that uses Fahrenheit-sized degrees. It starts at absolute zero (0 °R = -459.67 °F). Each rankine degree is the same size as one Fahrenheit degree. Rankine is used primarily in US engineering disciplines, particularly in thermodynamics, combustion science, and HVAC calculations where absolute temperatures are required in imperial units.
All temperature conversions can be performed using simple formulas. The key is knowing the relationship between any two scales. Here are the six essential conversion formulas:
Celsius → Fahrenheit: °F = °C × 9/5 + 32
Fahrenheit → Celsius: °C = (°F - 32) × 5/9
Celsius → Kelvin: K = °C + 273.15
Kelvin → Celsius: °C = K - 273.15
Fahrenheit → Rankine: °R = °F + 459.67
Rankine → Fahrenheit: °F = °R - 459.67
Question: Normal human body temperature is 37 °C. Express it in all four scales.
Question: A recipe calls for 350 °F. What is that in Celsius and Kelvin?
Question: Liquid nitrogen boils at 77.15 K. Convert to Celsius and Fahrenheit.
For a quick Celsius-to-Fahrenheit estimate, double the Celsius value and add 30. This gives reasonable accuracy for everyday temperatures: 20 °C → 2 × 20 + 30 = 70 °F (actual: 68 °F). For Fahrenheit to Celsius, subtract 30 and halve: 80 °F → (80 - 30) / 2 = 25 °C (actual: 26.7 °C). These shortcuts work best between 0–100 °C.
| Condition | °C | °F | K |
|---|---|---|---|
| Extreme Cold (Arctic) | -40 | -40 | 233.15 |
| Freezing Rain | -5 | 23 | 268.15 |
| Snow / Frost | 0 | 32 | 273.15 |
| Cool Spring Day | 10 | 50 | 283.15 |
| Comfortable Room | 22 | 71.6 | 295.15 |
| Warm Summer Day | 30 | 86 | 303.15 |
| Heat Wave | 40 | 104 | 313.15 |
| Extreme Desert Heat | 50 | 122 | 323.15 |
| Application | °C | °F |
|---|---|---|
| Slow Cooking / Dehydrating | 65–93 | 150–200 |
| Simmering Water | 85–96 | 185–205 |
| Boiling Water | 100 | 212 |
| Low Oven | 120–150 | 250–300 |
| Moderate Oven | 160–180 | 325–350 |
| Hot Oven | 190–220 | 375–425 |
| Very Hot Oven / Pizza | 230–260 | 450–500 |
| Broil / Grill | 260–290 | 500–550 |
| Deep Frying | 175–190 | 350–375 |
| Caramelizing Sugar | 160–177 | 320–350 |
| Phenomenon | °C | K | °R |
|---|---|---|---|
| Superconductor Transition (Nb) | -264 | 9.15 | 16.47 |
| Liquid Helium Boiling | -269 | 4.15 | 7.47 |
| Liquid Nitrogen Boiling | -196 | 77.15 | 138.87 |
| Dry Ice Sublimation | -78.5 | 194.65 | 350.37 |
| Lead Melting Point | 327 | 600.15 | 1080.27 |
| Aluminum Melting | 660 | 933.15 | 1679.67 |
| Iron / Steel Melting | 1538 | 1811.15 | 3260.07 |
| Tungsten Melting | 3422 | 3695.15 | 6651.27 |
Used worldwide for weather forecasts, cooking, medicine, and daily life. When a doctor measures your fever or a weather app shows today's high, Celsius is the standard in most countries. Its 0–100 water reference makes it intuitive for practical use.
The primary scale for weather, cooking, and HVAC in the United States. Americans set their thermostats, read oven dials, and check weather forecasts in Fahrenheit. Its finer degree resolution means a 1 °F change is smaller than 1 °C, giving more granularity for comfort settings.
The SI unit for scientific research across physics, chemistry, and astronomy. Used in the ideal gas law (PV = nRT), black-body radiation calculations, and color temperature for lighting and photography. Essential anywhere absolute temperatures matter, such as cryogenics and astrophysics.
Used in US-based thermodynamics, particularly for Carnot cycle efficiency, steam turbines, combustion engines, and HVAC system design. Engineers who work in imperial units but need absolute temperatures for calculations use Rankine instead of Kelvin.
For F → C, subtract 32 first, then multiply by 5/9. For C → F, multiply by 9/5 first, then add 32. Getting the order wrong is the most common conversion error.
Since -40 °F = -40 °C, you can verify your formula by plugging in -40. If both sides match, your conversion is correct.
A change of 1 °C equals a change of 1 K. The same is true for Fahrenheit and Rankine: a change of 1 °F equals a change of 1 °R. This makes differential (change) calculations straightforward.
The correct notation is 300 K, not 300 °K. This is an international convention because Kelvin is an absolute scale and an SI base unit.
If your conversion yields a negative Kelvin value, something went wrong. Absolute zero (0 K) is the lowest possible temperature. The same applies to Rankine.
One Celsius degree equals 1.8 Fahrenheit degrees. A "10-degree rise" means very different things depending on the scale: 10 °C rise = 18 °F rise.
Subtract 32 from the Fahrenheit value, then multiply by 5/9. The formula is: °C = (°F - 32) × 5/9. For example, 68 °F = (68 - 32) × 5/9 = 20 °C.
Absolute zero is the lowest theoretically possible temperature, where all molecular motion ceases. It equals 0 K, -273.15 °C, -459.67 °F, and 0 °R. It has never been achieved in a laboratory but has been approached to within billionths of a kelvin.
Kelvin is an absolute thermodynamic scale and the SI base unit of temperature. By international convention, temperatures in kelvin are written without a degree symbol (e.g., 300 K, not 300 °K). This distinguishes it from relative scales like Celsius and Fahrenheit.
-40 is the unique temperature where Fahrenheit and Celsius scales intersect. That is, -40 °F = -40 °C. You can verify this with the formula: °C = (°F - 32) × 5/9 → -40 = (-40 - 32) × 5/9 = -72 × 5/9 = -40.
Rankine is used primarily in US engineering and thermodynamics where an absolute temperature scale with Fahrenheit-sized degrees is needed. It appears in calculations involving the ideal gas law, Carnot efficiency, and heat transfer when working in imperial units.
At standard atmospheric pressure (1 atm), water boils at 100 °C, 212 °F, 373.15 K, and 671.67 °R. These values are exact reference points used to define the Celsius and Fahrenheit scales.
Add 273.15 to the Celsius value. The formula is K = °C + 273.15. For example, 25 °C = 25 + 273.15 = 298.15 K. The Kelvin and Celsius scales have identical degree sizes, so they differ only by a constant offset.
Celsius is the most widely used temperature scale globally. It is the standard in nearly every country except the United States, which uses Fahrenheit for everyday purposes. In science and engineering worldwide, Kelvin (the SI unit) and Celsius are both standard.
This calculator uses standard conversion formulas recognized by NIST and the International Bureau of Weights and Measures (BIPM). For critical scientific, medical, or industrial applications, always verify conversions against calibrated instruments and consult relevant standards for your field.