Pick up a penny. Then another. Then another. In fact, pick up a penny every second around the clock for the next 9 ½ years, and you'll...

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Pick up a penny. Then another. Then another. In fact, pick up a penny every second around the clock for the next 9 ½ years, and you’ll be holding nearly 300 million of them.

And why do that? Because it will help you get a sense of just how many people live in the United States — a number the Census Bureau says will pass 300 million sometime this month.

That’s enough people to fill 120,000 of Washington’s biggest ferries, or 721,000 Boeing 747s, or 4.7 million of Metro’s articulated buses.

Combining birth, death and immigration rates, the Census Bureau estimates the nation is growing by an average of one resident every 10 seconds.

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Hitting this mega-milestone is a fitting occasion to look at where we are today compared to 1915, when the U.S. population hit 100 million, and 1967, when it hit 200 million.

Ten defining characteristics of each year are shown in the chart at right. Here are some additional comparisons:

1915

Just how many is 300 million?

If 300 million fans wanted to see the Mariners play one regular-season game at Safeco Field, it would take 6,368 games to fit them all in — more than 78 seasons.

In 300 million steps, with a stride a yard long, you could walk around the world 6.8 times — assuming you could walk on water.

Once there are 300 million Americans, if every single one of them chips in $15.35, we might be able to replace the Alaskan Way viaduct with a tunnel.

If every man, woman and child in Washington state owned 24 pairs of shoes, we’d have a statewide shoe collection of more than 300 million.

World population : 1.8 billion

Washington governor: Ernest Lister

Washington population: 1.2 million

Average U.S. household size: 4.5

Gallon of milk: 36 cents

University of Washington enrollment: 3,225

Percentage of women in labor force: 23 percent

Women in U.S. Senate: 0

Percentage of U.S. residents over 24 with high-school diploma: 13.5 percent

U.S. at war: Had yet to enter World War I

1967

World population: 3.5 billion

Washington governor: Dan Evans

Washington population: 3.2 million

Average U.S. household size: 3.3

Gallon of milk: $1.03

University of Washington enrollment: 29,977

Percentage of women in labor force: 41 percent

Women in U.S. Senate: 2

Percentage of U.S. residents over 24 with high-school diploma: 51.1 percent

U.S. at war: Opposition grows to Vietnam War

2006

World population: 6.5 billion

Washington governor: Christine Gregoire

Washington population: 6.4 million

Average U.S. household size: 2.6

Gallon of milk: $3.06

University of Washington enrollment: 42,974

Percentage of women in labor force: 59 percent

Women in U.S. Senate: 14

Percentage of U.S. residents over 24 with high-school diploma: 85.2 percent

U.S. at war: War in Iraq enters fourth year

Times researcher Miyoko Wolf contributed to this report.

Jack Broom: 206-464-2222 or jbroom@seattletimes.com