Confidence Interval Calculator
Use this confidence interval calculator to calculate an interval around a sample estimate. Enter sample size, average, variation and confidence level and review a confidence interval around the estimate.
Assumes a known or estimated population standard deviation and a roughly normal sampling distribution (valid for n ≥ 30 by the Central Limit Theorem).
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How it works
CI = mean ± z × (σ ÷ √n)How to use the Confidence Interval Calculator
Start by entering sample size, average, variation and confidence level. Keep the units consistent and check that each value belongs to the same question.
The result gives a confidence interval around the estimate. The interpretation depends on the sample and statistical method. Use it as a guide and check any instructions, rules or professional advice that apply.