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Probability Calculator

Probability as a percentage, decimal and '1 in X' odds.

By CalcHub Editorial · Last reviewed

Quick answer

  • Formula: Single: P = Favorable ÷ Total · Combined (independent): P(A and B) = P(A) × P(B)
  • Worked example — Probability: 16.67% (full example below).

Probability Calculator

Worked example result
Probability16.67%
Probability (decimal)0.1667
Odds1 in 6

Rolling a specific number on a fair die: 1 ÷ 6 = 16.67%, or 1 in 6.

Diagram: how the Probability Calculator works — you enter Mode, Favorable outcomes (single mode), Total outcomes (single mode), Probability of event A (combined mode), Probability of event B (combined mode); it applies the formula Single: P = Favorable ÷ Total · Combined (independent): P(A and B) …; and the worked example gives Probabilit
How the Probability Calculator works — the inputs, the formula, and a worked example (Probability: 16.67%).

In single-event mode, enter favorable and total outcomes — rolling a 6 on a die is 1 favorable outcome out of 6 — to get the probability as a percentage, a decimal and in '1 in X' form.

In combined mode, enter the percentage probabilities of two independent events to find the chance that both happen. Independence matters: drawing two aces without replacement is not independent, so this combined mode does not apply to it.

The formula

Single: P = Favorable ÷ Total · Combined (independent): P(A and B) = P(A) × P(B)

Worked example

Rolling a specific number on a fair die: 1 ÷ 6 = 16.67%, or 1 in 6.

Worked example for the Probability Calculator: with Mode Single event (favorable ÷ total), Favorable outcomes (single mode) 1, Total outcomes (single mode) 6, the result is Probability: 16.67%; Probability (decimal): 0.1667.
The worked example, with the example values entered and the results they give.

The example is pre-loaded in the result panel — press Calculate with your own numbers to replace it.

Frequently asked questions

What does '1 in X' mean?

It is the reciprocal of the probability: an event with probability 0.25 happens on average once in every 4 tries — '1 in 4'. It describes long-run frequency, not a guarantee within any 4 tries.

When can I multiply two probabilities?

Only when the events are independent — the outcome of one does not change the other's odds. Two coin flips are independent; two cards drawn from the same deck without replacement are not.

Category: Everyday Life calculators

Sources & methodology

This calculator applies the formula shown on this page exactly as written, using the standard definitions for its inputs. Results are computed from the values you enter — no data is stored — and are rounded only for display.

Content last reviewed by CalcHub Editorial.

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