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Updated 2026-03-07 UTC
Sample Size for a Mean — Margin of Error Formula — GetCalcMaster
Compute sample size needed for estimating a mean with margin of error E: n ≈ (z·σ/E)². Includes practical notes and examples.
To estimate a population mean with a target margin of error E at a given confidence level, a common approximation is n ≈ (z·σ/E)², where σ is the SD of the outcome.
Important: Educational. For strict guarantees, match the sizing method to the estimator and sampling design.
What this calculator is
The Statistics Calculator is an interactive tool inside GetCalcMaster. It’s designed to help you explore scenarios, understand formulas, and document assumptions.
Key features
- Simple margin-of-error sizing for means
- Highlights the role of variability σ
- Shows how n scales with σ and E
Formula
n ≈ (z * σ / E)^2Quick examples
If σ doubles, n increases by ~4× (because n scales with σ²).If E halves, n increases by ~4× (because n scales with 1/E²).
How to use it (quick steps)
- Pick a confidence level (e.g., 95%) → get z.
- Estimate σ from pilot data or historical measurements.
- Choose margin of error E in the same units as the mean.
- Compute n ≈ (z·σ/E)² and round up.
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FAQ
Is this calculator official?
No. GetCalcMaster provides educational estimates and learning tools. Always verify against official definitions, documents, or professional advice.
Do you store my inputs on the server?
No. Calculations run locally in your browser. Optional remember/restore features (if enabled) use local browser storage.
Tip: For reproducible work, save your inputs and reasoning in Notebook.