She didn't even blink.

Barely had to think.

Dr. Debby Herbenick has heard the question before, and recited the answer too many times to count.

"Erect?" she said. "Between 5.1 and 5.8 inches."

There you have it.

But average penis size, Herbenick said, brushing her chestnut hair from her face, is actually a nice bell curve.

Some studies say the average is 5.1, others 5.3 and others 5.8, but roughly 80 percent of men fall within the range of 4 to 6 inches.

Herbenick would know. The 32-year-old academic is an associate director and assistant research scientist in the Department of Applied Health Science, and The Kinsey Institute for Research in Sex, Gender, and Reproduction at Indiana University. She is the voice behind the weekly online sex podcast, "Kinsey Confidential," and has studied such subjects as comparative condom size.

So she spends her time in a laboratory with a white coat and clipboard, watching people have sex?

"It's actually a completely normal work environment," she said, laughing. "It's never what people think of when it comes to unraveling sexual mysteries."

Herbenick's work is all about boring methodology -- interviews, questionnaires, online surveys, daily diaries -- yielding interesting findings. "For instance, it's known that women who are feeling very in love are more likely to perform oral sex on their husbands than those who are not feeling in love," she said. "And size really does matter when it comes to condoms."

But back to our subject.

I told the esteemed scientist I had heard the average male was longer.

She sighed. It's not uncommon for men to get the wrong figures.

Many studies rely on self-measurement, which is typically wrong (typically inflated). And the men who come across those incorrect results, she said, (like one study's average of 6.3 inches) often allow the results to feed their insecurities and get in the way of potential relationships. Who would have thought half an inch could do such damage?

Having talked sex all afternoon, I needed a smoke. But I couldn't figure out if I wanted a cigarette or a cigar. I didn't want to offend anyone, after all.

So I left Bloomington, and on the way I noticed a stallion in a field.

As I got to Indianapolis, I looked with renewed distaste at the city's central monument, one that puts all other local obelisks to shame.

And I tailgated a guy driving an F-350 with a "Size Matters" decal on the rear window.

I also began breaking the news to friends.

"Really?" they asked.

"5.1 inches, eh?" they said through prideful smiles.

However, when the women I told were surprised, I could sense the men in the room shrink. After all, if women expect the average to be bigger than 5.1 inches, what does that mean they expect from their men?

The drama, insecurity and pride began anew. I felt like a true sex columnist, and I thought of the words of Dr. Debby.

"It's fascinating and its heartening," she said. "I think that I learn just as much about what's going on in their minds as their bedrooms. I feel like I learn humanity."

Sizing each other up

• Average penis length (erect): 4 to 6 inches (some studies find 5.1, others 5.3 or 5.8, etc).

• Average penis girth (erect): 4 to 6 inches circumference.

• Average penis length (flaccid): 3.5 inches.

• Average penis girth (flaccid): 3 to 3.75 inches circumference.

• Average depth of the vagina (unaroused): 3 to 4 inches.

• Average depth of the vagina (aroused): 5 to 6 inches.

Source: Dr. Debby Herbenick, a sex researcher at IU and blogger at www.mysexprofessor.com