Conversion of Temperature

Quick Celsius (°C) / Fahrenheit (°F) Conversion:

measure/images/thermometer.js?mode=boxes

Type a value in either box

 

Or use the slider

Or the Interactive Thermometer

Or this method:

°C to °F Divide by 5, then multiply by 9, then add 32
°F to °C Deduct 32, then multiply by 5, then divide by 9

(Explanation Below ...)

Typical Temperatures

(only bold are exactly the same)

  °C °F Description
  220 430 Hot Oven
  180 360 Moderate Oven
  100 212 Water boils
  40 104 Hot Bath
  37 98.6 Body temperature
  30 86 Beach weather
  21 70 Room temperature
  10 50 Cool Day
  0 32 Freezing point of water
  −18 0 Very Cold Day
  −40 −40 Extremely Cold Day
(and the same number!)

16 is about 61
28 is about 82

Explanation

There are two main temperature scales:

They both measure the same thing (temperature!), but use different numbers:

Like this:

temperature freeze (0 vs 32) and boil (100 vs 212)

Looking at the diagram, notice:

And so, to convert:

from Celsius to Fahrenheit: first multiply by 180100, then add 32
from Fahrenheit to Celsius: first subtract 32, then multiply by 100180

180100 can be simplified to 95,
and 100180 can be simplified to 59, so we get this:

°C to °F:   Divide by 5, then multiply by 9, then add 32

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


Example: Convert 25° Celsius (a nice warm day) to Fahrenheit

First: 25° / 5 = 5
Then: 5 × 9 = 45
Then: 45 + 32 = 77° F

Example: Convert 98.6° Fahrenheit (normal body temperature) to Celsius

First: 98.6° − 32 = 66.6
Then: 66.6 × 5 = 333
Then: 333 / 9 = 37° C

We can swap the order of divide and multiply if we want, but don't change the add or subtract. So this is also OK:

Example: Convert 98.6° Fahrenheit to Celsius (again)

First: 98.6° − 32 = 66.6
Then: 66.6 / 9 = 7.4
Then: 7.4 × 5 = 37° C

(Same answer as before, was it easier or harder this way?)

We can write them as formulas:
Celsius to Fahrenheit:   (°C × 95) + 32 = °F
Fahrenheit to Celsius:   (°F − 32) × 59 = °C
 

Other Methods That Work

Use 1.8 instead of 9/5

9/5 is equal to 1.8, so we can also use this method:

Celsius to Fahrenheit:   °C × 1.8 + 32 = °F
Fahrenheit to Celsius:   (°F − 32) / 1.8 = °C


To make "×1.8" easier we can multiply by 2 and subtract 10%, but it only works for °C to °F:

Celsius to Fahrenheit:   (°C × 2) less 10% + 32 = °F

Example: Convert 20° Celsius (A nice day) to Fahrenheit

  • 20x2 = 40
  • less 10% is 40−4 = 36
  • 36+32 = 68° F

 

Add 40, Multiply, Subtract 40

Since both scales cross at −40° (−40° C equals −40° F) we can:

Like this:

Celsius to Fahrenheit:   Add 40, multiply by 9/5, then subtract 40
Fahrenheit to Celsius:   Add 40, multiply by 5/9, then subtract 40

Example: Convert 10° Celsius (A cool day) to Fahrenheit

  • 10+40 = 50
  • 50×9/5 = 90
  • 90−40 = 50° F

To remember 9/5 for °C to °F think "F is greater than C, so there are more °F than °C"

 

Quick, but Not Accurate

Celsius to Fahrenheit:   Double, then add 30
Fahrenheit to Celsius:   Subtract 30, then halve

Examples °C → °F:

Examples °F → °C:

 

temperature particles

Footnote: Temperature is a measure of how fast an object's particles are moving.

 

1041, 1042, 1043, 1044, 3724, 3725, 3726, 3727, 3728, 3729