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# Confidence interval online calculation

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Confidence interval calculator

Calculate the sample size of the mean, the mean, the standard deviation, and the confidence interval for the given input for the selected confidence level.

Standard deviation, variance online calculator

Use the formula:

$$If (n>=30)$$,

$$CI = x ± Zα/2 × (σ/√n)$$

$$If (n<30)$$,

$$CI = x ± tα/2 × (σ/√n)$$

Here,

x = average

σ = standard deviation

α = 1 - (confidence level /100)

Zα/2 = value in the Z-table

tα/2 = t-value in the table

CI = confidence interval.