Confidence Interval Calculator
Calculate confidence intervals for a population mean using your sample statistics. Choose from 90%, 95%, or 99% confidence levels to determine the range within which the true mean likely falls.
A confidence interval gives a range of values that is likely to contain the true population parameter.
Formula:
CI = x̄ ± z × (σ / √n)
Where:
- x̄ = sample mean
- z = z-score for the chosen confidence level
- σ = standard deviation
- n = sample size
Common z-scores:
- 90% confidence: z = 1.645
- 95% confidence: z = 1.96
- 99% confidence: z = 2.576
A wider interval provides more confidence but less precision. Increasing the sample size narrows the interval without sacrificing confidence.