First and foremost may be the question of relevancy of the numbers of men who are capable of bench pressing 300+ pounds. Is it relevant to you if you don't compete in powerlifting? If you are a competitive powerlifter or an advanced weight lifter you already know that a 300+ pound bench press is a difficult accomplishment. Also relevant to the question is to consider the size and age of the lifter achieving a 300+ pound bench press. If you are 22-years old and weigh 250 pounds, or 50-years old and weigh 175 pounds effects the relevancy of the ultimate achievement. A better comparison of strength in general would be multiples of bench press to body weight with .9 to 1 being average, 1.5 to 1.75 intermediate, 1.8 to 2 being advanced and 2.25+ being extraordinary (without bench shirt or performance enhancements). In general, in only rare cases have bench presses at or above 2.75 x body weight been recorded without the use of bench shirts or steroids. The use of either in powerlifting defeats the purpose of measuring the limits of human strength.
Consider for a moment that for an average male to advance from a 160 pound single rep bench press to a single rep with 300 pounds means that the same male would need to increase his bench press from a single rep with 160 pounds to 260 pounds for about 5-6 reps or more, not a simple task. However there are articles published on the Internet that indicate that a 50#-100# increase in the bench press can be achieved in as little as 3 weeks to a few months! Really!
Also relevant is that the average male experiences maximum strength between approximately 18-30 years of age although many record bench presses are achieved well beyond the age of 30 but strength is beginning to decline in the 30's and 40's. Therefore, most males would more likely achieve a 300+ pound bench press between the ages of 18-40. However, obviously not all males regularly participate in physical activities and far fewer weight train seriously. According to the U.S. census there was an estimated 90,000,000 males in the United States in 2009 between the ages of 17-59. U.S. data of males between 15-59 years of age regularly participating in regular physical activities is conflicting but estimates generally range from 16%-25%. The percentage is skewed by younger males, interpretations of physically active, frequency of physical activity and duration of physical activity by this age group.
The percentage of all males indicating that they "regularly" weight train as their physical activity is approximately 13% of all reported physically active males or about 2.4 million males (17-59) in the U.S. This seems to be a reasonable projection.
However, of the 2.4 million males regularly weight training only about 6% report weight training sessions with durations of between 45 minutes and 1+ hours (.205*.13*.06 = .002665) or about 144,000 of the 90,000,000 total males in this age group. This is about 1 in 625 of all males 17-59 or about 1 in 16 males who regularly weight train. This also seems to be a reasonable projection. Regular frequency of training sessions (45 minutes to 1+ hours) is a subjective factor but generally reported to be 2-3+ times per week. This level of training would be necessary to achieve a 300+ pound bench press in the vast majority of males.
For the vast majority of the remaining segment of the male population (17-59) weight training is for the purpose of general physical conditioning or to participate in seasonal non-professional sports such as football, basketball, running, track and field, wrestling, and other sports where the ultimate result is to seasonally improve overall conditioning, not significant strength levels associated with powerlifting, Olympic lifting or bodybuilding where a 300+ bench press is a goal.
It is further believed that of this male population an estimated 25% has the necessary objective, physical attributes and genetics (excluding most males below the body weight of 135 pounds and considering that most males above 60 years of age would be less likely to have the physical capabilities or interest) necessary to achieve a 300+ pound bench press. Therefore, using this calculation about 39,600 (.25*158,000) males in the U.S. would likely have the necessary interest, investment of time, strength and physical potential to perform a regulation bench press of 300+ pounds without using any special equipment including bench shirts but not excluding males that may be using performance enhancing drugs. This is an average of about 792 males per U.S. state with some states such as Texas, California and Illinois having a much higher proportion and other states such as Alaska, Delaware or Connecticut far fewer based on overall male population.
As a comparative sampling, considering that large highly equipped metropolitan weight gyms such as a Gold's with 600+ locations and 3,000,000 total members (48% male) nationwide or about 5,000 registered members per location will often have fewer than 10 males (less than 1/2% of total male membership) that perform a regulation bench press with 300+ pounds with optimum equipment and environment to weight train seems to be consistent with the calculations performed for the larger male population.
Consider that even if the 300#-349# calculations shown below were in error by even a factor of three times the male population shown (an improbable possibility) the number of men bench pressing less than 300 pounds would still be roughly 99.9%. If you have other reliable statistics to consider to improve the possible accuracy of this model please forward for review.
Good luck with your training!
300#-349# - 27,000-31,000 (1 in 3,000 males 16-60+)