use scale
a millimeter
You must first decide what you want to measure about the rice grains: their length, circumference, mass, weight, volume, color, elasticity, etc.
Personally, I would measure the length of a grain of rice in millimeters.
It is not possible to give a sensible answer to the question. A square metre is a measure of area in 2-dimensional space whereas the mass of rice depends on the volume - a 3-dimensional measure - of rice. The height of the pile of rice will affect the mass of rice.
Use dry measure measuring cup.
use scale
Yes, you can use the water displacement method to measure the volume of rice grains. Fill a graduated cylinder with water to a certain level, then carefully add the rice grains to the water. The increase in water volume after adding the rice grains will give you the volume of the rice grains.
a millimeter
You must first decide what you want to measure about the rice grains: their length, circumference, mass, weight, volume, color, elasticity, etc.
Personally, I would measure the length of a grain of rice in millimeters.
mass is best measured by fluid volume displacement
To measure a grain of rice when the mass is too small to be read on a centigram balance, you can use a more sensitive balance such as a milligram or microgram balance. These scales are capable of measuring extremely small masses and would be able to accurately measure the mass of a single grain of rice.
You can use a precision scale that measures in milligrams, place the grain of rice on the scale, and note the weight displayed. Alternatively, you could use a balance scale and known weights to find the weight of the rice by comparing it to the known weights.
You would measure a rice plant (or perhaps the length of a rice field) in meters. You would generally measure a container of rice grains (for cooking or eating) in kilograms, unless you were concerned about how much space it would take up on a shelf or something like that.
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It is not possible to give a sensible answer to the question. A square metre is a measure of area in 2-dimensional space whereas the mass of rice depends on the volume - a 3-dimensional measure - of rice. The height of the pile of rice will affect the mass of rice.