Banzhaf Index Calculator


The Banzhaf Index is a measure of the power distribution in a voting system. This index helps to determine how critical a player’s vote is in making a decision. This article will guide you through understanding the Banzhaf Index, how to use it, the formula, an example calculation, FAQs, and the importance of this index in voting power analysis.

How to Use

To use the Banzhaf Index Calculator, input the weights of each voter and the quota required for a decision. Click the “Calculate” button to see the power index for each voter.


The Banzhaf Index for each voter is calculated by determining the number of times a voter’s vote is critical in changing an outcome from a loss to a win. The formula can be summarized as follows:

  1. List all possible coalitions of voters.
  2. For each coalition, check if the total weight meets or exceeds the quota.
  3. For each voter, count how many times their vote is critical (i.e., without their vote, the coalition would not meet the quota).
  4. Normalize these counts by dividing by the total number of critical votes for all voters.

Example Solve

Suppose we have a voting system with three voters A, B, and C with weights 4, 2, and 1 respectively, and a quota of 4. To calculate the Banzhaf Index:

  1. Identify all coalitions.
  2. Determine critical votes.
  3. Calculate the index.

This process involves several steps, which the calculator can automate for you.


What is the Banzhaf Index used for?
The Banzhaf Index is used to measure the power of voters in decision-making processes, particularly in political science and corporate governance.

How does the Banzhaf Index differ from the Shapley-Shubik Index?
While both indices measure voting power, the Banzhaf Index considers each voter’s ability to change the outcome of a vote, whereas the Shapley-Shubik Index also takes into account the order of voters.

Can the Banzhaf Index be applied to non-political scenarios?
Yes, it is applicable in any situation where decisions are made by a weighted voting system, including corporate board decisions and cooperative game theory.


The Banzhaf Index provides a quantitative measure of the influence of each voter in a decision-making process. By using this calculator, you can easily determine the power distribution among voters in any weighted voting system.

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