pounds
Newtons.
kilo-newtons.
Try grams
grams
That depends what aspect of the adult you want to measure: the adult's height, mass, weight, volume, albedo, intelligence (no SI unit for that!), etc.
Pounds
You would use the metric unit "kilograms" to measure the weight of a bag of groceries.
You would use the unit of measurement called "kilograms" or "pounds" to measure the weight of a car.
You would use the metric unit "kilograms" to measure the weight of a sack of peaches.
You would typically use a unit of weight, such as grams or ounces, to measure a cherry.
A millinewton. NOT a gram, which a measure of mass, not of weight.
grams
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pounds
Newtons.
The most appropriate unit of weight for a computer would be in pounds.