Pounds.
The liter is commonly used. For a small bottle, milliliters might also be used.
That one!
The SI unit would be grams, however considering a blade of grass is pretty small I would probably measure it in mg, milligrams.
Metric ruler
You would use meters.
On a ruler using the metric system, you would typically find units such as centimeters and millimeters. These units are used for measuring length and are based on powers of ten for easy conversion. The metric system is widely used in many countries around the world.
Kilogram
The gram.
The kilogram.
Millimeter
liter
Millimetres.