It will depend on the designers of the aircraft.
Most vintage and American aircraft will be measured in inches. Where as more modern and European aircraft will use millimetres and the metric system.
The reason these units of measurement are quite small even on a large passenger aircraft like an Airbus A380 is that everything has a design sheet, commonly known as a blueprint. Each component, panel, window and part that goes up to make an aircraft is designed individually. These component parts are all then given a higher level of drawing that shows how the small parts make a larger part, then finally how the larger parts make the aircraft as a whole.
An example of this is there will be a design sheet for a wingtip navigation light, showing its dimensions. Then there will be a design sheet for the wing, showing where that navigation light fits onto the wing. Then finally a main drawing showing how the wing fits on the aircraft. This level of detail can go all the way down to a drawing for each screw that holds the navigation light lens onto the navigation light body.
But regarding of how small or large the item is, from a single screw to a whole aircraft, the drawings will all be in the same unit of measurement.
Probably the metric ton which is 1000 kilograms - about 2200 pounds (hence metric ton).
Alternatives would be the Megagram (same as 1000 kilograms; capital M please) and the Gigagram (1 million kilograms).
The weight of just about every airplane, no matter what its
size and capacity, is expressed in pounds.
I would use feet and inches to measure an aircraft
You would use metres(M)
meters
As a potato chip is light weight I would use grams and milligrams.
You would probably measure a keyboard in centimeters (cm).
A meter stick would be one. A metric tape measure would be another.A measuring tape.a rulerA meter stickyou can use a metric tape or a yardstick or a metre trundle wheel and finally a metre stickA tape measure, calibrated in meters.A meterstickusually a metric measuring tape.
Liters
What metric unit would you use to measure a computer keyboard
kilometre
you would measure it in kilograms
kilograms.
gram
The weight of the box would be measured in grams.
A scale
Mass is measured in kilograms.
milli-gram
The metric unit for measuring human weight is actually the Newton (N). Newton's are a measure of force and weight is the product of the acceleration of gravity and an objects mass. The metric unit for measuring human mass is the kilogram (kg).
Every country in Europe uses the metric system, meaning they would measure weight in kilograms, grams, etc.
A gram would be an appropriate measure for its mass.
It depends on whether you want to measure mass or weight so your question needs to be more specific.