Confidence Level Calculator

A confidence interval gives a range likely containing the true population value. 95% CI: if the same study were repeated 100 times, ~95 intervals would contain the true value

The calculator uses the standard published formula for confidence interval gives a range likely containing the true population value. Results are accurate to the precision of the inputs you provide. For financial, medical, or legal decisions, always verify with a qualified professional.

This calculator works with inches, percentages. You can enter values in the units shown — the calculator handles all conversions internally.

The core formula is: Margin of error = z × √(p(1−p)/n). Each step in the calculation is shown so you can verify the result manually.