I stand by that using tailor’s tape is the best for measuring the penis length and girth.
Tailor’s tape is soft and flexible, so naturally it’s perfect for girth measurements since you need to measure an ovular/circular cylinder. But while others say a rigid wooden or plastic ruler should be used for length, I disagree.
Penises are rarely perfectly straight, the vast majority of penises have some kind of curvature - be it a curve to the left or right, or an upward or downward curve. Tailor’s tape measures the length of the penis and can account for these curvatures, a rigid ruler cannot, thus tape measurements are more accurate than ruler measurements.
To measure girth, find what seems to be the thickest part of your erect shaft, then starting at 0 on the tailor’s tape, hold the 0 mark in place with one hand while you use your other hand to wrap the tape around your shaft. Wrap the tape around once until the tape meets the 0 point again. The number that meets the 0 is your erect girth measurement.
To measure length, place the tape on the top side of your erect penis and use one hand to hold 0 at the base where your pubes are. Then use the other hand to glide the tape along your erect length until you get to the very tip of the top side of your penis. The number at that point is your erect length. If your penis has any curvature, be sure to make the tape follow the contours of your penis curvatures exactly.