This summary is based on the LifeStyles condoms Cancun data set:

Mean length (n=300): 5.877 inches (14.928 cm) erect (assuming bone pressed)
Standard deviation: 0.825 inches (2.096 cm)
Analysis:

Lengths at each standard deviation:

5th sd below mean: 1.752 inches
4th sd below mean: 2.577 inches
3rd sd below mean: 3.402 inches
2nd sd below mean: 4.227 inches
1st sd below mean: 5.052 inches
Mean: 5.877 inches
1st sd above mean: 6.702 inches
2nd sd above mean: 7.527 inches
3rd sd above mean: 8.352 inches
4th sd above mean: 9.177 inches
5th sd above mean: 10.00 inches

Frequency in population:

1.752 inches: 1 in 3.5 million
2.577 inches: 1 in 31,574
3.402 inches: 1 in 741
4.227 inches: 1 in 44
5.052 inches: 1 in 6
5.877 inches: 1 in 2
6.702 inches: 1 in 6
7.527 inches: 1 in 44
8.352 inches: 1 in 741
9.177 inches: 1 in 31, 574
10.00 inches: 1 in 3.5 million

Rank in population, by percentile:

1.752 inches: 0.0000003rd percentile
2.577 inches: 0.000032nd percentile
3.402 inches: 0.14th percentile
4.227 inches: 2.3rd percentile
5.052 inches: 15.9th percentile
5.877 inches: 50th percentile
6.702 inches: 84.1st percentile
7.527 inches: 97.7th percentile
8.352 inches: 99.86th percentile
9.177 inches: 99.9968th percentile
10.00 inches: 99.99997th percentile