Keep in mind that it should be slightly more than this, considering that those measurements are usually slightly more than the exact foot/half foot.
but, approximately 40 u.k./imperial gallons - 42 u.s. gallons - 164 liters
So, the difference is small. but, add an inch to each of those measurements, and it is closer to 45/48/188 respectively.
I think mine actually measures 13.5" in width, but it is very common to say a 55 u.s. gallon tank is 4' x 1' x 1.5' ... even though that is just rounded off figures. A tank that size would only be 45 u.s. gallons ... which I know it isn't since I have filled it with 5 gallon buckets
1 u.s. gallon equals approximately 0.83 u.k./imperial gallons.