convert unit of measure mpg->lp100km

Question

So, I have the problem to convert mpg to lp100km.

I have tried to calculate them by hand, given that 1 mile = 1.60934 km and 1 gallon = 3.78541 litres, and it yields me like: 1 mpg = 235.133 lp100km

However, when I searched for the conversion online, there are different values and it makes me confused whether my answer is right or not.

I have also tried to convert back, what I mean here is lp100km->mpg. But why did I get the same result, i.e. 1 lp100km = 235.133 mpg

Can anyone help me with this?

Thanks!

$1$ mile per gallon gives something very close to what you got. With the conversion numbers of the post (which I have not checked) I get about $235.215$. Perhaps you rounded during the calculation. — André Nicolas, Sep 13 '14 at 04:47
The kind of precision we used is meaningless. Fuel consumption figures, in say miles per gallon, are at best rough estimates. — André Nicolas, Sep 13 '14 at 04:56

score 1 · Accepted Answer · answered Sep 13 '14 at 05:16

Simple unit analysis: \begin{align*} 1 \frac{\text{mile}}{\text{gallon}} \times \frac{1.60934}{1} \frac{\text{km}}{\text{mile}} \times \frac{1}{100} \frac{\text{100 km}}{\text{km}} \times \frac{1}{3.78541}\frac{\text{gallon}}{\text{L}} = 0.00425142 \frac{\text{100 km}}{\text{L}}, \end{align*} and so, 1 mpg is equivalent to $\frac{1}{0.00425142} = 235.215 \frac{\text{L}}{\text{100 km}}$.

However, keep in mind that mpg and L/100 km are inverse units, so 10 mpg would be equivalent to 23.5215 L/100 km.

convert unit of measure mpg->lp100km

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