**Simple Conversions of Celsius and Fahrenheit Temperature Scales**

### 1. Standard Conversion

**°F to °C :** Deduct 32, then multiply by 5, then divide by 9

**°C to °F :** Multiply by 9, then divide by 5, then add 32

### 2. Use 1.8 instead of 9/5

**°C to °F : ** °C × 1.8 + 32 = °F

**°F to °C : ** (°F − 32) / 1.8 = °C

### 3. Add 40, Multiply, Subtract 40

**°C to °F : **Add 40, multiply by 9/5, then subtract 40

**°F to °C :** Add 40, multiply by 5/9, then subtract 40

### 4. Fast Conversion but NOT Accurate :

**°C to °F :** Double, then add 30

**°F to °C :** Subtract 30, then halve

## What Temperature are Celsius and Fahrenheit Value Same?

**The formulas for converting between degree Celsius and degree Fahrenheit are:**

**°F = (°C * 9/5) + 32**

**°C = (°F – 32) * 5/9**

To find the temperature when both are equal, we use an old algebra trick and just set ºF = ºC and solve one of the equations.

°C = (°C * 9/5) + 32

°C – (°C * 9/5) = 32

-4/5 * °C = 32

°C = -32 * 5/4

°C = -40

°F = (°F * 9/5) + 32

°F – (°F * 9/5) = 32

-4/5 * °F = 32

°F = -32 * 5/4

°F = -40

So the temperature when both the Celsius and Fahrenheit scales are the same is -40 degrees.

### Reason :

Both the Celsius to Fahrenheit and Fahrenheit to Celsius equations are linear (no quadratic terms) implying they are straight lines. They have different slopes and are non-parallel with a single solution. If we solve for this solution or plot both the lines, we see that the intersect at (-40,-40). The fact that they intersected at a whole number is purely coincidental.

Anders Celsius actually defined his temperature scale exactly the opposite way that everybody thinks he did. He originally defined 0 as the boiling point and 100 as the freezing point. This was changed around the time of Celsius’ death in 1744, by two eminent contemporary scientists working independently of each other — Frenchman Jean-Pierre Christin and Celsius’ fellow Swede Carolus Linnaeus. Since this matched the arrangement of the other scales then in use (Fahrenheit and Reaumur, mostly — Kelvin and Rankine were about a century away still), the proposals were widely accepted and we still use 0 for freezing and 100 for boiling today.

**Also Read : Peltier Effect Theory**