Use a rigid ruler or measuring tape
Measure when the penis is fully erect for consistency
For length, place the ruler on the top side of the penis
Press the ruler gently into the pubic bone at the base
Measure from the pubic bone to the tip of the glans
Do not include the foreskin beyond the tip
For girth, wrap a flexible measuring tape around the thickest part of the shaft
If using string for girth, mark where it overlaps and measure the string with a ruler
Take measurements more than once and use the average
Measure in the same position and under similar conditions each time
Record the result in inches or centimeters