What metric unit should you use for a spoon?

Answer 1

The answer depends on what characteristic you wish to measure:

• mass - grams
  
• weight - milli newtons
• length - milllimetres
• volume - millilitres

and so on.

Answer 2

That depends what property of the spoon you want to measure: for instance its length, its mass, its weight, its albedo, its electrical conductivity, etc.