How to Do Temperature Conversion
Between Fahrenheit and Celsius in your head
Part 1, using the two regular formulas:
= (
i) Conversion from Fahrenheit to Celsius using formula
= (
for
example, given 700 F, we subtract 32 from 70 to get 38, then half of 38 to get 19, and
then 19 + 1.9 + 0.19 = 21.10 C. If only for estimating, you just add 19 by 1.9 = 210C. Note
the key is
(
, so
(
(
(
(
(
(
(
(
= 19 + 1.9 +0.19 +0.019 +… = 21.111…
ii) Conversion from Celsius to Fahrenheit using formula °F =
for
example, given 300C, we multiply 30 by1.8 = , to get 540, then plus 32 to get 860 F.
To memorize the two regular formulas, the most important thing is to understand that
the value of certain temperature in Fahrenheit is always greater than Celsius ( one
exception, -400 F = -400 C), so when converting Fahrenheit to Celsius the value
decreases, so subtract 32 first, then multiply by (<1), while converting Celsius to
Fahrenheit, the value increases, so multiply (>1) then add 32.
Part 2, using another two formulas,
(
(
The advantages of using these two new formulas are:
1) Always add 40 to the given temperature whatever to convert from Fahrenheit to
Celsius or from Celsius to Fahrenheit.
2) Multiply by if conversion is from Fahrenheit to Celsius (since the value
decreases)
3) Multiply by
if conversion is from Celsius to Fahrenheit (since the value
increases)
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4) Always subtract 40 from the answer from 3) whatever to convert from
Fahrenheit to Celsius or from Celsius to Fahrenheit.
5) These two new formula have the same format which are much easier to
memorize, and do by you head quickly.
Example 1, 20
=?
Step1, add 40: 40 + 20 = 60,
Step2, multiply by
: 60 (
Step3, subtract 40 from 108: 108 - 40 = 68
, so 20
= 68
, so 30
= 86
Example2, 95
Step1, Plus 40: 95 + 40 =135,
Step2, multiply by
( )
Step3, subtract 40: 75 - 40 = 35
so 95
Example3, 70
Step1, Plus 40: 70 + 40 =110,
Step2, multiply by
( )
Step3, subtract 40: 61.1 - 40 = 21.1
Example 4, 30
so 70
=?
Step1, add 40: 40 + 30 = 70,
Step2, multiply by
: 70 (
Step3, subtract 40 from 108: 126 - 40 = 86
If you are interested in deriving these two new formulas Please continue to read the
next page.
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(
Derive Formula
(
and
Based on either one of the regular formula we fill the following table:
°F
-1000
-1480
-800
-1120
-600
-760
-400
-400
-200
- 40
00
320
200
680
400
1040
1000
2120
We find that temperature in -400 F = -400C.
This pattern enables us to change the regular formulas as follows,
1) The regular formula
(
= (
(
(
= (
(
(
(
(
2) The regular formula
= (
)
(
(
(
(
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Academic Success Centre
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