Centimeters
a meter stick.
Scientist would use milimeters.
The answer will depend on whether you want the mass of a pencil, its weight, its length, width, volume. You may want to measure its colour!
grams (for their mass), centimetres (for length), millimetres (for thickness/height), possibly Mohs scale for hardness.
Pencil lead is very narrow. Millimeter can be used to measure it.
a ruler!
You would measure it in centimeters.
A ruler would do the trick.
Centimeters
length
Centimeters
A ruler or tape measure.
a meter stick.
Mm
You can measure small lengths in millimeters. Length of a pencil, pen, eraser, length and width of a paper, sheet etc. can be measured in millimeters.
Scientist would use milimeters.
The length of a pencil. your waist/chest measurement the dimensions of a table