Confidence Interval Width Planner Calculator

Plan sample size required for a target confidence-interval width using confidence level and estimated standard deviation.

Confidence Level (%)

Estimated Std Dev (sigma)

Target CI Width

Core Formula

n = (z * sigma / ME)^2 where width = 2 * ME

Use this as a planning and validation aid, then confirm assumptions with your context.

Your Results

Calculated

Required Sample Size
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Primary output

Margin of Error

Secondary output

z-score Used

Verification metric

Planning Note

Interpretation

Enter values and calculate to get scenario outputs.

This calculator is designed for practical analysis and fast scenario testing. Use conservative assumptions first, then compare improved scenarios.

Study-friendly tools for checking assumptions and recording samples.

Useful when you want intuition behind the formulas.

Sketch distributions when tables feel opaque.

Helps translate plotted results into readable scales.