GRAMS
Neither of those units will produce a very convenient number. But of the two, the kilogram is the better choice.
Ounces.
Depending on the model and material; you can measure the mass using a suitable balance.
Metres
Depending on your location, it might be difficult to come up with a meter stick or a tape measure that displays centimeters and meters. It's probably better to measure it in feet and inches and convert it to metric mathematically.
A microgram.
Potatoes are sold by the kilogram.
A thermometer.
distance
Centimeters
kilograms
you would measure it in kilograms