Temperature Converter

Convert between Celsius, Fahrenheit, Kelvin, Rankine, and Réaumur — the one conversion that needs offsets and scaling, not a single factor.

Temperature

°C, °F, K, °R, Réaumur

From

Result

33.8

°F = (°C × 9/5) + 32

Popular conversions

What Is a Temperature Converter?

A temperature converter translates a temperature reading between scales — Celsius to Fahrenheit, Celsius to Kelvin, and the rarer Rankine and Réaumur. Temperature is the odd one out among unit conversions: most units convert by multiplying a single factor, but temperature scales have different zero points as well as different step sizes, so converting requires both a multiplication and an addition.

This converter handles the offset-and-scale math for you. Celsius and Kelvin share a step size but differ by 273.15 in their zero point; Fahrenheit has both a different zero and a different step (9/5 the size of a Celsius degree). Kelvin starts at absolute zero — the coldest possible temperature — which is why scientists use it for any calculation involving the actual energy of particles.

This is one category of the full Unit Converter — pair it with our percentage calculator or scientific calculator for related everyday maths.

How Temperature Conversion Works

Offset plus scale, not just a factor

Unlike length or weight, temperature scales differ in both their zero point and their degree size, so you can't convert by one multiplier — you scale, then shift.

Celsius ↔ Fahrenheit

°F = °C × 9/5 + 32. The 9/5 reflects Fahrenheit's smaller degree, and the +32 accounts for its different zero. They cross at −40°, where both scales read the same.

Celsius ↔ Kelvin

K = °C + 273.15. Same degree size, just a shifted zero: Kelvin's zero is absolute zero, the point of minimum molecular motion.

Why Kelvin for science

Gas laws, thermodynamics, and radiation formulas need an absolute scale starting at true zero. Using Celsius in them would give wrong ratios because its zero is arbitrary.

Core Temperature Formulas

Temperature conversion always combines scaling and an offset. These are the conversions this tool applies.

Celsius → Fahrenheit

°F = °C × 9/5 + 32

Scale by 9/5 for the smaller degree, then add 32 for the offset zero.

Celsius → Kelvin

K = °C + 273.15

Same degree size; add 273.15 to shift the zero to absolute zero.

Fahrenheit → Celsius

°C = (°F − 32) × 5/9

Remove the 32 offset first, then scale by 5/9 to reach Celsius degrees.

How to Use the Temperature Converter

1
Enter the temperature
Type the reading you want to convert — it can be negative, since temperatures go below zero on most scales.
2
Choose the 'from' scale
Pick Celsius, Fahrenheit, Kelvin, Rankine, or Réaumur as your starting scale.
3
Choose the 'to' scale
Select the scale you want the result in, or swap the two to reverse direction.
4
Read all scales together
The all-units view shows the temperature on every scale at once — useful for checking a weather, oven, or lab reading against an unfamiliar scale.

Key Temperature Concepts

Absolute zero

0 Kelvin (−273.15 °C, −459.67 °F), the theoretical point of minimum thermal energy. Nothing can be colder, which is why Kelvin has no negative values.

Celsius

A scale with 0° at water's freezing point and 100° at its boiling point (at sea level). The everyday standard in most of the world.

Fahrenheit

A scale with 32° freezing and 212° boiling, giving 180 degrees between them. Still standard for weather and cooking in the US.

The −40° crossover

Celsius and Fahrenheit read the same value at −40°. A handy sanity check: if your conversion gives −40 °C ≠ −40 °F, the math is wrong.

Real-World Temperature Conversions

🌡️

Weather forecasts

20 °C is a pleasant 68 °F; 100 °F is a hot 37.8 °C. Travellers convert between the two scales whenever they cross between metric and US regions.

🍗

Oven and cooking temps

A 180 °C oven is 356 °F (recipes usually round to 350 °F); a safe chicken temp of 165 °F is 74 °C. Cooking spans both scales.

🤒

Body temperature

Normal body temp is 37 °C or 98.6 °F; a 38.5 °C fever is 101.3 °F. Thermometers and medical advice switch scales by country.

🔬

Scientific calculations

Gas-law and thermodynamics problems need Kelvin: 25 °C room temperature is 298.15 K. Using Celsius in these formulas gives wrong ratios.

❄️

Freezing and boiling

Water freezes at 0 °C / 32 °F and boils at 100 °C / 212 °F at sea level — the reference points that define the everyday scales.

🚀

Extreme environments

Liquid nitrogen boils at −196 °C (77 K); the Sun's surface is about 5,778 K. Kelvin keeps these vast ranges on one positive scale.

Best Practices for Temperature Conversion

✓Apply the offset, not just the scale. Temperature isn't a single-factor conversion. Forgetting the +32 (or +273.15) offset is the classic error — you must scale and shift.
✓Use Kelvin for any physics formula. Gas laws, efficiency, and radiation math require an absolute scale starting at true zero. Plug in Kelvin, never Celsius or Fahrenheit.
✓Check against −40°. Celsius and Fahrenheit meet at −40°. If your conversion doesn't preserve that fixed point, you've made an arithmetic slip.
✓Mind that temperature can be negative. Unlike length or mass, temperatures go below zero on Celsius and Fahrenheit. Keep the sign through the calculation.
✓Don't convert temperature differences like readings. A change of 10 °C equals a change of 18 °F (no +32 offset applies to differences). Offsets apply to readings, not intervals.

Common Temperature Conversion Mistakes

Forgetting the +32 offset

Multiplying °C by 9/5 without adding 32 (or omitting the offset entirely) is the most frequent temperature error. Scale and shift are both required.

Using Celsius in gas laws

Thermodynamic formulas need absolute temperature. Plugging in Celsius instead of Kelvin gives nonsensical ratios — e.g. dividing by a near-zero or negative number.

Applying offsets to differences

A temperature change of 5 °C is 9 °F, not 41 °F. The +32 offset applies only to absolute readings, never to intervals.

Dropping the sign on cold readings

Negative temperatures are real. Losing the minus sign turns a −5 °C frost into a warm +5 °C, a 10-degree error.

Why Temperature Conversion Matters

Temperature governs weather, cooking, health, manufacturing, and nearly all of physical science — and it's the one common conversion where a naïve 'multiply by a factor' approach fails. Because the scales differ in both zero point and degree size, an offset error doesn't just shift the answer slightly; it can put a fever in the normal range, an oven 30 degrees off, or a science calculation wildly wrong.

The stakes climb in technical work: thermodynamic and gas-law formulas are only valid on an absolute scale, so using Celsius where Kelvin is required produces results that are not just imprecise but meaningless. A converter that handles the scale-and-offset math correctly — and exposes Kelvin alongside the everyday scales — keeps both the kitchen and the lab honest.

Built for travellers, cooks, healthcare workers, students, and scientists moving between Celsius, Fahrenheit, and Kelvin.

Linear unit factors follow the BIPM SI brochure, the NIST Guide to the SI, and ISO 80000. Currency rates load live from open.er-api.com; crypto prices from CoinGecko. See our methodology and editorial policy. Educational only — not certified for regulated trading, settlement, medical, or aerospace use.

Temperature Converter FAQs

Multiply the Celsius value by 9/5 (1.8) and add 32: °F = °C × 9/5 + 32. So 20 °C = 20 × 1.8 + 32 = 68 °F. The 9/5 accounts for Fahrenheit's smaller degree and the +32 for its different zero point — both steps are required.

Subtract 32 first, then multiply by 5/9: °C = (°F − 32) × 5/9. So 98.6 °F = (98.6 − 32) × 5/9 = 37 °C. Remove the offset before scaling, not after, or the answer will be wrong.

Add 273.15: K = °C + 273.15. So 25 °C = 298.15 K. Celsius and Kelvin use the same degree size, so there's no scaling — only the offset that moves the zero point to absolute zero.

Absolute zero is 0 Kelvin, equal to −273.15 °C or −459.67 °F. It's the theoretical temperature at which molecular motion is minimal, and nothing can be colder — which is why the Kelvin scale never goes negative.

Because thermodynamic formulas — gas laws, efficiency, blackbody radiation — depend on absolute temperature measured from true zero. Celsius has an arbitrary zero (water's freezing point), so using it in those equations gives incorrect ratios. Kelvin starts at absolute zero, so it works directly.

At −40°, where −40 °C equals −40 °F exactly. It's the single point where the two scales coincide, and a useful check: any correct C↔F conversion must preserve it.