Decision tool

Coin Flip

One flip, or as many as you like. Genuinely 50/50 — flip ten thousand times here and the totals will differ by well under a percent.

Result

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Heads share this session — the tick marks a fair coin's 50%

This session's flips (clears when you close the tab)

How this coin flip works

There is no image of a coin being spun and no animation to guess at. Each flip draws a number from crypto.getRandomValues(), the random number generator built into your browser by the Web Crypto API and seeded by your operating system. Heads is returned if that number falls in the lower half of its range, tails otherwise. Because the two halves are the same size, each result has exactly the same probability.

That matters more than it sounds. Math.random(), which most simple web tools use, is a much weaker generator: its output is drawn from 32 bits of state and successive values are predictable if you know enough of them. For deciding where to eat tonight, that is a distinction without a difference. For anything involving money, access keys or a contest you might win, use a real coin. This page is for the first category.

Flip many coins at once

The Flip 10 and Flip 1,000 buttons exist because a single flip tells you nothing. Flips are independent: the previous result has no effect on the next one, so a run of six heads is not a signal that tails is "due". A coin has no memory, and neither does this one.

Use Count heads vs tails to run a proper test. Enter a number of flips and the page counts both outcomes and runs a chi-square test on the difference, which is the standard way to check whether a set of results looks consistent with a fair coin. With ten thousand flips you will almost always land within a couple of percent of 50/50 — and occasionally you will not, in either direction, because that is what variance looks like.

What to use this for

  • Choosing between two options you have already weighed equally
  • Breaking a tie in a game where neither player deserves the edge
  • Deciding who pays for the next round, in the knowledge that it does not matter
  • Settling arguments about whether something is a 50/50 call — by establishing that it is

For more than two options there is the wheel of fortune; for a whole group of people, the card pull.

Related

Privacy and terms

Nothing you roll is ever sent to us, and no account exists to send it to. The privacy policy sets out the detail, including the cookies that advertising may set; the terms of service cover what these tools can and cannot do for you. Questions go to contact@grunners.vip.