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.
A metric ruler measures in inches and centimeters.
Metric ruler
You would use meters.
Grams.
Millimeter
The kilogram.
Millimetres
Millimetres.
a millimeter