"Goblin weights at most 1/2 of a washing Machine.".
Don't you see how silly the imperial system is?
Okay, if you actually want to debate this, then lets debate this.
The Metric system was created to create a uniform system that was based on 'universal' measurements, that were just as arbitrary in the end as imperial units, because a meter isn't actually a meter, because they measured the earth wrong. However, that doesn't matter because everyone agrees what a meter is. If we were ACTUALLY going to make a universal system, then we should have started with the Planck Length, not something as silly as the circumference of the Earth.
How about celsius? Why is absolute zero -273.15ºC? The Kelvin Scale would have been better way to go.
The only advantage of Metric over imperial is that it's based on factors of 10, however, from a WRITERS perspective, this SUCKS.
Why? Simple. IT'S BORING.
When you write, a sign of a good story is avoiding using the same word more than once. The less times you have to use a word in a paragraph, a chapter, or even a book, the better. Synonyms are the life blood of a writer and the truth is metric is HORRIBLE from a writer's use as far as story elements are concerned, because the UNIFORMITY quickly makes your story start to read like a engineer's manual or instructions on how to assemble your Ikea Furniture.
However, using Furlongs-Firkins-Fortnights along with stones, Hammers, football fields, country mile, graves, jiffy, Hiroshima bombs, and good old fashion Tons are far more interesting then Meters, Grams, and seconds.
For example, I once described a MC as as strong as Six Korean War Jeeps, as big as an adult Male Kangaroo, and as intelligent as a slightly concussed Rene Descartes.
Or I could have said he could lift 6,300 Kg, he was 1.88 meters tall, and had an IQ of 117.
Which reads better?
If you want to go in universe, the history of units of measurements are based on local agreements. The Foot used to be the actual size of the foot of the local ruler, and could change as you got a new king. If you are having a story that isn't based in the modern age, then you will want to use imperial as it will sound more natural. If you want to go all out, actually work out what sort of whacky units of measurements they would use.
Remember, the pint is still used for buying beer because a Liter is too much, and half a liter sounds stupid when you sat it out loud.
Units of measurements are what gives a setting character. Metric is designed to create uniformity and destroy cultures. it has it's place when you are building a rocket, but it has little place in a historical setting. Now if I was doing something in a sci-fi setting, I'd put everything in Metric, for no other reason then to help set the mood of how dystopian the setting is.