PA_M7_S4_T1_English
to Metric Length Transcript
Often I am given measurements in English standard units and I need to
know what they are in metric units. The conversion of length measurements
from English standard to metric all starts from this very first
conversion you see here that says 1 inch is approximately equal to 2.54
cm.
This is a very important conversion and if you don't remember anything
else, remember this one because all the rest of these conversions can be
arrived at simply from using the first one.
Let's see how that looks, I want to convert 12 inches into meters. To do
this conversion, I have 2.54 cm/inch, that's my first conversion. Then I
have 1 m for every 100 cm. When I do this multiplication I get 0.3048 m,
which is exactly what's given in this table.
Let's look at one other, let's look at 36 inches converted into meters. I
have 2.54 cm per inch, I have one meter for every 100 cm, I do the math
and I end up with 0.9144 meters which is exactly what I have my table.
Sometimes as we use approximations like this we get a little off track,
so depending on the accuracy you want, some of my conversion factors may
be less accurate than starting from the very beginning. Let's look at
this conversion I want to convert 3 miles into kilometres. I'm going to
start by converting miles into feet, 5280 feet per mile, I have 12 inches
in every foot, and I have 2.54 cm in every inch. Each meter is 100 cm,
and each kilometer is 1000 meters. I've set this up the long way, but I
get all my units canceling, which works really nicely, and I'm left with
simply having everything in terms of kilometres. When I do this
multiplication I get a result that says that this is equal to 4.828032
kilometres.
Again it's an approximation, so I could say that this is very close to
4.828 km, if I want to; however let's look at the shorter conversion.
3 miles is 1.6093 kilometres per mile for my conversion ratio. When I do
that multiplication I get 4.8279. Now, when I round this, I still get the
approximation of 4.828, but notice that there is quite a difference, if
I'm looking at third or fourth digit accuracy, between this value and
this value. It's not enough to make things very, very different if I'm
driving down the road and calculating distances, but depending on my
calculation I may want to introduce fewer errors earlier on, by going
back to the very first approximation and not use something that's
actually increased the amount of error I have just through the conversion
process.
This is one of the conversions I mentioned in the introduction that is
extremely powerful and universal. If you know this you can get everything
else without having to memorize an entire table
of conversion factors.