Flip a Coin

Reading your session statistics

The session panel keeps three numbers: heads, tails and your best streak, plus a bar for the heads to tails ratio and a strip of the last 30 results. These are fun to watch, but they swing more than most people expect. In 30 fair flips, a split of 18 to 12 or more lopsided in either direction happens about 36% of the time. A best streak of four or five in a row within a few dozen flips is ordinary. The ratio only settles close to 50% after hundreds of flips, which is the law of large numbers at work.

The best streak counts the longest run of the same side, heads or tails. Over 100 flips, a run of at least seven of the same side turns up about 54% of the time, so a long streak is not a sign that anything is off. The statistics live only on the open page, so reloading it starts a fresh session.

Reset the stats whenever you start a new experiment, such as a classroom test, so earlier flips do not blend into your new count.

Using a coin to choose between more than two options

A single coin decides between two choices, but two flips can decide fairly between four. Label the outcomes heads-heads, heads-tails, tails-heads and tails-tails, assign one option to each and flip twice. Each outcome has a chance of exactly 1 in 4. For three options, use the same method and flip both coins again if you get the fourth outcome. Every remaining result stays equally likely, so the choice is still fair. Best of three is also fair: whichever side wins two flips first wins the decision. Each side still has a 50% chance, because the extra flips are just as random as the first.

Famous coin tosses in American history

The name of Portland, Oregon was settled by a coin toss in 1845. Asa Lovejoy wanted to name the town after Boston and Francis Pettygrove wanted Portland, after the city in Maine. Pettygrove won. The coin they used, an 1835 large cent, is known as the Portland Penny and is kept by the Oregon Historical Society.

In December 1903 Wilbur and Orville Wright tossed a coin at Kitty Hawk to decide who would make the first attempt at powered flight. Wilbur won, but his attempt on December 14 failed. Orville made the first successful flight three days later, on December 17.

Heads, tails and how US coins are oriented

US coins are struck in what collectors call coin alignment. If you hold a coin by its top and bottom edges and turn it over top to bottom, the reverse is right side up. Turn it side to side instead and the reverse appears upside down. Many other countries use medal alignment, where the reverse is upright after a side-to-side turn. When you pick up a coin after a toss, this is why the tails side often appears upside down. Lincoln on the cent faces right, while Jefferson, Roosevelt, Washington and Kennedy face left.

Frequently asked questions