Unlike metric, all the different imperial measurements are just combinations of different kinds of initially unrelated measurement systems. So a gallon has abso

Unlike metric, all the different imperial measurements are just combinations of different kinds of initially unrelated measurement systems. So a gallon has absolutely nothing to do with foot, miles are a completely different measurement system than feet, pounds and so on. Needing to know the weight of a cubic hectare of water and then how many gallons that is, is not a common issue. Metric does give you a system that can quickly calculate these things comparatively.