It depends on what characteristic of the grassshoper you want to measure - its mass, its length, the volume of its chirp, the frequency of its colour. etc.
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To ad to the above by giving the scientifically appropriate units, and in that order, they are:
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For mass, the gramme (g),
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For length, the millimetre (mm)
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For chirp volume, the "deciBel re 20micro-Pascals" or 20dB re 20µPa for short.
(This is often called just the 'deciBel' for shortness, provided the context is clear, as the decibel is a logarithm of a ratio, not a linear unit of a single thing like the gramme or millimetre. It is the standard unit for airborne sounds, related to the 0dB set at the 20 micro-Pascals minimum sound pressure-level audible to humans with fully-healthy hearing. If you calculate our 0dB pressure's linear equivalent, it is a staggeringly tiny 1 / 5000 000 000 of 1 Atmosphere! Don't say you didn't ask... :-) )
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Frequency of chirp: Hertz (Hz)
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Frequency of colour: possibly Hz but light is more often measured in wavelength instead, when it would be the nanometre (nm), where 1nm = 1 X 10^(-9) metres. I am not sure on this point but the choice may reflect (!) the SI definition of the Metre as so-many wavelengths of sodium light; bright yellow, in the middle of our visible spectrum.
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What else?
Walking or flying speed? Metres/second (m/s, sometimes expressed as m.s^(-1) ).
Pity this text editor doesn't include superscripts to allow typing such units properly, so clearly!
You would use the metric unit "kilograms" to measure the weight of a bag of groceries.
You would use the metric unit "kilograms" to measure the weight of a sack of peaches.
A gram would be an appropriate measure for its mass.
You would most likely use milliters.
Grasshoppers typically weigh only a few grams, usually less than 1 gram. It would be more convenient to weigh a grasshopper in grams rather than kilograms due to its small size.
Millimeter
You would use the metric unit "kilograms" to measure the weight of a bag of groceries.
You would use the metric unit "kilograms" to measure the weight of a sack of peaches.
A refrigerator would typically be measured in kilograms (kg) in terms of weight in the metric system.
Mass and weight are two different things: you cannot measure the mass of your weight. That is like talking about the temperature of your height - it makes no sense.
A gram would be an appropriate measure for its mass.
gram
You would most likely use milliters.
The weight of the box would be measured in grams.
A scale
Mass is measured in kilograms.
Grasshoppers typically weigh only a few grams, usually less than 1 gram. It would be more convenient to weigh a grasshopper in grams rather than kilograms due to its small size.