Celsius to Fahrenheit
Convert celsius (°C) to fahrenheit (°F). Both measure thermal measurement, and the conversion comes up in weather, cooking, science work.
The Formula
``
°F = °C × 9/5 + 32
`
Temperature scales have different zero points, so this is not a simple multiplication —
you cannot convert a temperature *difference* the same way you convert a temperature.
Conversion Table
| Celsius | Fahrenheit |
|---|---|
| -40 °C | -40 °F |
| 0 °C | 32 °F |
| 10 °C | 50 °F |
| 20 °C | 68 °F |
| 25 °C | 77 °F |
| 30 °C | 86 °F |
| 37 °C | 98.6 °F |
| 50 °C | 122 °F |
| 100 °C | 212 °F |
The Other Direction
| Fahrenheit | Celsius |
|---|---|
| -40 °F | -40 °C |
| 0 °F | -17.7778 °C |
| 10 °F | -12.2222 °C |
| 20 °F | -6.6667 °C |
| 25 °F | -3.8889 °C |
| 30 °F | -1.1111 °C |
| 37 °F | 2.7778 °C |
| 50 °F | 10 °C |
| 100 °F | 37.7778 °C |
What Each Unit Is
Celsius (°C) — a scale on which water freezes at 0 °C and boils at 100 °C at standard pressure. Proposed by Anders Celsius in 1742 — originally inverted, with 0 as boiling — and flipped after his death.
Fahrenheit (°F) — a scale on which water freezes at 32 °F and boils at 212 °F. Set by Daniel Fahrenheit in 1724 using a brine freezing point as zero and human body temperature near 96.
A Sense of Scale
Room temperature is 20–22 °C- Body temperature is 37 °C
- A hot summer day is 30 °C
- Room temperature is 68–72 °F
- Body temperature is 98.6 °F
- A hot summer day is 86 °F
Watch Out For
- Temperature scales have different zero points, so conversion is not a multiplication. Use °F = °C × 9/5 + 32.
- The offset matters: −40 is the one temperature where the two scales agree, and a *difference* of 1 °C is 1.8 °F, not 33.8.
In Code
`javascript
const celsiusToFahrenheit = (value) =>
value * 9/5 + 32;
`
Where This Conversion Comes Up
Weather- Cooking
- Science
- HVAC
- Medicine
Why This Is Not a Multiplication
Every other unit conversion is a ratio: doubling the input doubles the output. Temperature
is not, because the two scales put their zero in different places.
Celsius Fahrenheit Water freezes 0°C 32°F Water boils 100°C 212°F Zero means the freezing point of water the freezing point of a brine solution Fahrenheit could reproduce in 1724 Degrees between freezing and boiling 100 180
So the conversion has two parts: scale the degree size by
1.8000, then shift
the origin.A Temperature and a Temperature Difference Are Different Things
This is the error that reaches production code. Converting "it is 20°C" and
converting "it rose by 20°C" are not the same operation:
Quantity Conversion An absolute temperature Scale and shift A difference or a rate Scale only
A rise of 1°C is a rise of 1.8°F, not 33.8°F. Weather APIs, thermostat deltas and materials
data all carry differences, and a converter applied blindly to them is wrong by the offset.Negative Values and Absolute Zero
Celsius and Fahrenheit both go below zero; Kelvin does not. Absolute zero is 0 K, −273.15 °C
and −459.67 °F, and no temperature below it exists — a converter returning a negative Kelvin
value has been given an impossible input.
−40 is the one temperature where Celsius and Fahrenheit agree. It falls out of solving
x = x × 9/5 + 32, and it is a useful sanity check: if your conversion does not produce
−40 °F for −40 °C, the formula is wrong.
In Code
`javascript
// Absolute temperatures
const cToF = (c) => c * 9 / 5 + 32;
const fToC = (f) => (f - 32) * 5 / 9;
const cToK = (c) => c + 273.15;
// Differences — scale only, never shift
const deltaCToF = (dc) => dc * 9 / 5;
`
Note that Kelvin takes no degree sign: it is written 293 K, never 293 °K`.