speculative fiction writers i am going to give you a really urgent piece of advice: don't say numbers. don't give your readers any numbers. how heavy is the sword? lots. how old is that city? plenty. how big is the fort? massive. how fast is the spaceship? not very, it's secondhand.
the minute you say a number your readers can check your math and you cannot do math better than your most autistic critic. i guarantee. don't let your readers do any math. when did something happen? awhile ago. how many bullets can that gun fire? trick question, it shoots lasers, and it shoots em HARD.
you are lying to people for fun. if you let them do math at you the lie collapses and it's no fun anymore.
YOU GET IT