Easy ways to do rough conversions between some imperial units to the metric system

Note: These are not meant to be exact conversions, but to give you an approximation that is easy to do mentally and that will be good for most situations that do not require exact precision.

Temperature: From Fahrenheit to Celsius

(step 1) Subtract 32 from the Fahrenheit temperature
(step 2) Divide the result by 2

Example: 50°F -> (step 1) 50-32 = 18 -> (step 2) 18/2 = 9
So 50°F convert to roughly 9°C

If you want to be more precise, multiply the result of step 1 by 5/9 instead of dividing it by 2. But dividing by two should be a good enough approximation for most purposes.

Temperature: From Celsius to Fahrenheit

Just do the opposite of the °F to °C conversion explained above.

(step 1) Multiply the Celsius temperature by 2
(step 2) Add 32 to the result

Example: 9°C -> (step 1) 9*2 = 18 -> (step 2) 18+32 = 50
So 9°C convert to roughly 50°F

Weight: From pounds (lbs) to kilograms (kg)

(step 1) Subtract 10% from the lbs measure
(step 2) Divide the result by 2

Example: 60 lbs -> (step 1) 60 - (10% of 60, which is 6) = 54 -> (step 2)  54/2 = 27
So 60 lbs convert to approximately 27 kg

You can also just divide the lbs measure by 2.2, but I find that it is much easier to do the 2 steps above if you are doing it mentally.

Weight: From kilograms (kg) to pounds (lbs)

Just do the opposite of the lbs to kg conversion explained above.

(step 1) Multiply the kg measure by 2
(step 2) Add 10% to the result

Or you can just multiply by 2.2

Example: 20 kg -> (step 1) 20*2 = 40 -> (step 2)  40+(10% fo 40, which is 4) = 44, or simply 2.2*20 = 44
So 20 kg convert to approximately 44 lbs

Length: From feet to meters

(step 1) Multiply the feet measure by 3
(step 2) Divide the result by 10

Example: 10 feet -> (step 1) 10*3 = 30 -> (step 2) 30/10 = 3
So 10 feet convert to approximately 3 meters
 
Or if you find it easy to do decimal multiplications mentally, just multiply the feet measure by 0.3 (or 0.28 if you want to be more exact).


Length: From meters to feet

(step 1) Multiply the meters measure by 10
(step 2) Divide the result by 3

Example: 3 meters -> (step 1) 3*10 = 30 -> (step 2) 30/3 = 10
So 3 meters convert to approximately 10 feet

Or if you find it easy to do decimal multiplications mentally, just multiply the meters measure by 3.3 (or 3.28 if you want to be more exact).

Area: From squared feet to squared meters

(step 1) Subtract 10% from the squared feet measure
(step 2) Divide the result by 10

Example: 500 squared feet -> (step 1) 500 - (10% of 500, which is 50) = 450 -> (step 2)  450/10 = 45
So 500 squared feet convert to approximately 45 squared meters

Or if you find it easy to do decimal multiplications mentally, just multiply the squared feet measure by 0.09 (0.093 if you want to be more exact)


Area: From squared meters to squared feet

(step 1) Multiply the squared meters measure by 10
(step 2) Add 10% to the result

Example: 50 squared meters -> (step 1) 50*10 = 500 -> (step 2)  500 + (10% of 500, which is 50) = 550
So 50 squared meters convert to approximately 550 squared meters

Or if you find it easy to do decimal multiplications mentally, just multiply the squared feet measure by 10.8