Confidence Interval Calculator
Compute confidence intervals for a population mean or proportion at 80-99.9% confidence using the z-distribution.
MATHCompute a confidence interval for either a population mean (with known/estimated standard deviation) or a population proportion. Supports 80%, 90%, 95%, 98%, 99%, and 99.9% confidence levels.
CI for mean: x̄ ± z × (σ/√n). CI for proportion: p̂ ± z × √(p̂(1−p̂)/n). Z-values for 95% CI is 1.96; for 99% is 2.576. Wider CI = more confidence, less precision. Doubling sample size narrows CI by factor of √2.
Confidence Interval Calculator
Compute a confidence interval for either a population mean (with known/estimated standard deviation) or a population proportion. Supports 80%, 90%, 95% (default), 98%, 99%, and 99.9% confidence.
Uses normal (z) distribution. For small samples (n < 30) with unknown σ, use a t-distribution. For proportions, the Wilson score interval or Clopper-Pearson exact interval are more reliable when np or n(1−p) is small.