Depending on the size of it id say either a 15cm ruler or a 30cm ruler.
A ruler would do the trick.
Centimeters
Centimeters
Centimeters
A ruler or tape measure.
If you have to measure the pencil to a couple decimal places i would suggest a micrometer and a dial caliper.
centimeter
grams (for their mass), centimetres (for length), millimetres (for thickness/height), possibly Mohs scale for hardness.
To find the volume of a pencil, you can approximate it as a cylinder. Measure the diameter of the pencil to find the radius, and then measure its length. Use the formula for the volume of a cylinder, ( V = \pi r^2 h ), where ( r ) is the radius and ( h ) is the height (length of the pencil). Calculate the volume using these measurements.
Depending on the size of it id say either a 15cm ruler or a 30cm ruler.
You could use either centimeters or millimeters, but probably centimeters.
a ruler