How do I convert Celsius to Fahrenheit?

Multiply the Celsius value by 9/5 (or 1.8) and add 32. Example: 100 °C × 9/5 + 32 = 212 °F.

How do I convert Fahrenheit to Celsius?

Subtract 32 from the Fahrenheit value and multiply by 5/9. Example: (212 − 32) × 5/9 = 100 °C.

What is 100 °C in Fahrenheit?

100 °C equals 212 °F — the boiling point of water at standard atmospheric pressure.

What is 0 K in Celsius?

0 Kelvin is absolute zero, equal to −273.15 °C or −459.67 °F. Nothing in the universe can be colder.

What is the Rankine scale used for?

Rankine (°R) is an absolute temperature scale based on Fahrenheit degrees. It's used in some US engineering fields, especially thermodynamics and aerospace.

What is the Réaumur scale?

Réaumur (°Ré) sets 0 at the freezing point of water and 80 at its boiling point. It was once popular in Europe and is still occasionally used in cheese and syrup production.

Why can't Kelvin or Rankine be negative?

Both are absolute scales that start at absolute zero — the theoretical lowest temperature possible. A negative value would mean a temperature below absolute zero, which is physically impossible.

At what temperature do Celsius and Fahrenheit read the same?

At −40°. −40 °C equals exactly −40 °F. It's the only point where the two scales intersect.

Which temperature scale do scientists use?

Kelvin is the SI unit for temperature and is preferred in scientific work. Celsius is used in everyday science and most countries; Fahrenheit is mainly used in the United States.

Is this converter accurate enough for cooking and science?

Yes. All formulas use the exact internationally defined factors and double-precision math. Results are rounded to 6 significant digits for readability.

Does it work offline?

Yes. The converter runs entirely in your browser, so once the page is loaded it works without an internet connection.

Can I share my conversion via URL?

Yes. The URL updates with ?value= and ?scale= as you convert. Copy the URL to share an exact result with anyone.

All tools

Free · No sign-up

100% private · Offline-ready

5 scales

Temperature Converter — Celsius, Fahrenheit, Kelvin, Rankine & Réaumur

Convert any temperature across five scales with absolute precision. Built for travelers, students, scientists, engineers and cooks — every result comes with the exact formula and a shareable URL.

Convert temperature

Type a value, pick a scale, hit Convert — the URL updates so you can share the exact result.

Presets:

Quick swap:

100°Cequals

Celsius

Fahrenheit

°F

212

Kelvin

373.15

Rankine

°R

671.67

All 5 scales6 sig. digits

Scale	Value	Formula
Celsius °C source	100°C	identity
Fahrenheit °F	212°F	°F = °C × 9/5 + 32
Kelvin K	373.15K	K = °C + 273.15
Rankine °R	671.67°R	°R = (°C + 273.15) × 9/5
Réaumur °Ré	80°Ré	°Ré = °C × 4/5

Tip: the URL updates as you convert — copy it to share the exact result.

Supported Temperature Scales

Five scales — the three you'll meet every day and two used in specialized engineering and historical contexts.

Name	Symbol	Water freezes	Water boils	Where used
Celsius	°C	0	100	Most countries, daily life, science
Fahrenheit	°F	32	212	USA, Bahamas, Cayman Islands
Kelvin	K	273.15	373.15	SI unit, science, astronomy
Rankine	°R	491.67	671.67	US engineering, thermodynamics
Réaumur	°Ré	0	80	Historical Europe, cheese, syrup

How to Use the Converter

Type the temperature you want to convert into the Value field.
Choose its source scale from the dropdown (°C, °F, K, °R or °Ré).
Click Convert — the URL updates and every scale appears in the results grid with the exact formula.
Use Quick swap to flip between popular pairs like °C ↔ °F.
Click a Preset (absolute zero, body temp, water boils, …) to load common reference points instantly.

Conversion Formulas

Celsius ↔ Fahrenheit

°F = °C × 9/5 + 32
°C = (°F − 32) × 5/9
Example: 100 °C × 9/5 + 32 = 212 °F

Celsius ↔ Kelvin

K = °C + 273.15
°C = K − 273.15
Example: 25 °C + 273.15 = 298.15 K

Fahrenheit ↔ Kelvin

K = (°F − 32) × 5/9 + 273.15
°F = (K − 273.15) × 9/5 + 32
Example: (98.6 − 32) × 5/9 + 273.15 = 310.15 K

Rankine ↔ Fahrenheit / Kelvin

°R = °F + 459.67
K = °R × 5/9
Example: 32 °F + 459.67 = 491.67 °R

Réaumur ↔ Celsius / Fahrenheit

°Ré = °C × 4/5
°F = °Ré × 9/4 + 32
Example: 20 °C × 4/5 = 16 °Ré

Réaumur ↔ Kelvin

K = °Ré × 5/4 + 273.15
°Ré = (K − 273.15) × 4/5
Example: 80 °Ré × 5/4 + 273.15 = 373.15 K

Common Reference Points

Memorize these and you'll rarely need the calculator at all.

Reference	°C	°F	K	°R	°Ré
Absolute zero	-273.15	-459.67	0	0	-218.52
Water freezes	0	32	273.15	491.67	0
Room temperature	20	68	293.15	527.67	16
Body temperature	37	98.6	310.15	558.27	29.6
Water boils	100	212	373.15	671.67	80

Quick Reference Tables

Celsius to Fahrenheit

°C	°F
-40	-40
-20	-4
-10	14
0	32
10	50
20	68
25	77
30	86
37	98.6
50	122
75	167
100	212

Fahrenheit to Celsius

°F	°C
0	-17.7778
14	-10
32	0
50	10
68	20
77	25
86	30
98.6	37
100	37.7778
150	65.5556
200	93.3333
212	100

Use Cases

Travel & weather

Quickly translate forecasts between °C and °F when crossing borders.

Cooking & ovens

Convert recipe oven temperatures between °C and °F without guessing.

Science & lab

Switch between K, °C and °F for experiments, dosing and reporting.

HVAC & engineering

Use Rankine and Fahrenheit for US thermodynamics calculations.

Medicine

Compare body temperature readings — 37 °C / 98.6 °F is normal.

Everyday

Settle the ‘what's 70 °F in real degrees?’ argument once and for all.

The Story Behind Each Scale

Celsius (1742, Anders Celsius) — originally inverted, with 0 as boiling and 100 as freezing. It was flipped soon after to today's form and is now the global standard.

Fahrenheit (1724, Daniel Gabriel Fahrenheit) — based on a brine freezing point (0 °F) and human body temperature (~96 °F). Still standard in the United States.

Kelvin (1848, Lord Kelvin) — an absolute scale starting at 0 K, the lowest possible temperature. The official SI unit, no degree symbol needed.

Rankine (1859, William Rankine) — absolute scale built on Fahrenheit degrees. Used in US engineering, especially thermodynamics and aerospace.

Réaumur (1730, René-Antoine Ferchault de Réaumur) — 0 to 80 between water's freezing and boiling points. Once popular across Europe; today mostly a curiosity, but still seen in some cheese, syrup and brewing recipes.

Accuracy & Rounding

All conversions use the exact internationally defined constants and double-precision arithmetic. Results are rounded to six significant digits for readability; the underlying calculation is effectively exact for everyday and scientific use.

Privacy & Performance

Every conversion runs locally in your browser. Nothing you type leaves your device — no logs, no analytics on your values, no server round-trip. The page weighs only a few KB and works offline once loaded.