Temperature Conversion: How to Convert Between Celsius, Fahrenheit, and Kelvin

Temperature is one of the few measurements the world never agreed on. A recipe from London bakes at 180, a recipe from New York bakes at 350, and a physics textbook reports the same oven in the 400s — all describing similar heat in three different scales. Celsius, Fahrenheit, and Kelvin each carve up temperature differently, and moving between them trips up cooks, travelers, students, and scientists alike. The good news is that the conversions are exact, simple, and built on the fixed physical behavior of water and the absolute floor of cold. This guide lays out the formulas, works an example for each pairing, and points out where people most often go wrong.

What the Three Scales Are and Why They Differ

Each scale was anchored to different reference points, which is why their numbers look so unalike.

Celsius sets 0 at the freezing point of water and 100 at its boiling point (at standard pressure). Its 100-degree span makes it intuitive and it is the everyday standard almost everywhere outside the United States.

Fahrenheit places water's freezing point at 32 and its boiling point at 212, a 180-degree span. The finer degrees give more granularity without decimals, and it remains the day-to-day scale in the US.

Kelvin starts at absolute zero — the theoretical point where molecular motion stops — and uses degrees the same size as Celsius degrees. There are no negative kelvins, which is exactly why science uses it: thermodynamic equations need a scale with a true zero. Water freezes at 273.15 K.

Two facts explain every conversion. First, Celsius and Fahrenheit have different zero points and different degree sizes (a Fahrenheit degree is 5/9 the size of a Celsius degree). Second, Celsius and Kelvin share a degree size but are offset by exactly 273.15.

How to Convert Between the Scales

Here are the six exact conversions:

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
Fahrenheit to Kelvin: K = ((°F − 32) × 5/9) + 273.15
Kelvin to Fahrenheit: °F = ((K − 273.15) × 9/5) + 32

The Celsius–Fahrenheit conversions need both a scaling step (the 9/5 or 5/9 factor for the different degree sizes) and a shift step (the 32 for the different zero points). The Celsius–Kelvin conversions need only the shift, because the degrees are identical. The Fahrenheit–Kelvin pair simply chains the two together: convert to Celsius in the middle, then on to the target.

Worked example — a few everyday conversions.

Convert 25 °C (a pleasant room) to Fahrenheit:

1. 25 × 9/5 = 45

2. 45 + 32 = 77 °F

Convert 98.6 °F (body temperature) to Celsius:

1. 98.6 − 32 = 66.6

2. 66.6 × 5/9 = 37 °C

Convert 25 °C to Kelvin:

1. 25 + 273.15 = 298.15 K

Convert 350 °F (a hot oven) to Kelvin, chaining through Celsius:

1. 350 − 32 = 318

2. 318 × 5/9 = 176.67 °C

3. 176.67 + 273.15 = 449.82 K

You can run any value between any two scales instantly with the Temperature Converter rather than chaining the steps by hand.

Practical Use and Common Mistakes

These conversions show up constantly. Travelers read a 30 °C forecast and want to know it is a warm 86 °F. Cooks adapt a 200 °C European recipe to a 392 °F American oven. Students convert lab readings into Kelvin before plugging them into a gas-law equation, where only an absolute scale gives correct results.

A handful of errors recur.

Forgetting the offset before scaling. When going from Fahrenheit to Celsius, subtract 32 first, then multiply by 5/9. Doing it in the wrong order — multiplying before subtracting — gives a badly wrong answer. The reverse direction must add 32 last.

Using 273 instead of 273.15. For rough mental math the rounded offset is fine, but precise scientific work needs the full 273.15. The 0.15 matters when accuracy does.

Mixing up the 9/5 and 5/9 factors. Heating up the number (Celsius to Fahrenheit) multiplies by the larger 9/5; cooling the number down (Fahrenheit to Celsius) multiplies by 5/9. A quick sanity check: 100 °C should land at 212 °F, not 32.

Expecting negative Kelvin. If a conversion produces a temperature below 0 K, something is wrong — absolute zero is the floor, and nothing colder exists.

Confusing a temperature with a temperature difference. A change of 5 °C equals a change of 9 °F and a change of 5 K. When converting an interval rather than a reading, apply only the scaling factor, never the 32 or 273.15 offset.

Conclusion

Temperature conversion looks fiddly only because three scales sit at different starting lines. Once you see that Celsius and Fahrenheit differ in both zero point and degree size, while Celsius and Kelvin differ only by a fixed shift, every formula falls into place. Subtract before you scale, keep your factors straight, remember the 273.15 offset for absolute work, and treat differences differently from readings. With those habits, moving a number from one scale to another is reliable arithmetic rather than a guessing game.

Key Takeaways

• Two scales, two adjustments: Celsius–Fahrenheit conversions need both a 9/5 (or 5/9) scaling and a 32-degree shift; Celsius–Kelvin needs only the 273.15 shift

• Mind the order: When converting Fahrenheit to Celsius, subtract 32 before multiplying by 5/9; reverse the order going the other way

• Use the full offset: Round to 273 for mental math, but use 273.15 for any precise scientific conversion with the Temperature Converter

• Differences are not readings: To convert a temperature change rather than a temperature, apply only the scaling factor and drop the 32 or 273.15 offset