Sample Size Calculator

Study Type

Proportion StudySurveys, polls, prevalence studiesMean EstimationContinuous variables, measurementsGroup ComparisonCompare two groups or treatments

Expected Proportion (p)Expected proportion (0-1). Use 0.5 for maximum variability if unknown.

Margin of Error (%)Desired margin of error as percentage (e.g., 5 for ±5%).

Confidence LevelStatistical confidence in your results.

Population Size (optional)Total population size. Leave blank for large/infinite populations.

Population Standard Deviation (σ)Known or estimated population standard deviation.

Margin of Error (E)Maximum acceptable margin of error.

Confidence LevelStatistical confidence in your results.

Tip: If σ is unknown, use a pilot study or literature estimates.

Effect Size (Cohen's d)Expected effect size. Small=0.2, Medium=0.5, Large=0.8

Statistical PowerProbability of detecting the effect if it exists.

Significance Level (α)Maximum acceptable Type I error rate.

Test TypeDirection of expected difference.

Quick Examples

Survey

95% confidence, 5% margin

Clinical Trial

80% power, medium effect

Market Research

90% confidence, 3% margin

Margin of Error Calculator: Calculate the margin of error for your existing sample size and survey results.

Sample Size (n)Number of responses or participants in your study.

Population Proportion (%)Response percentage. Use 50% for most conservative estimate.

Confidence LevelStatistical confidence in your results.

Population Size (optional)Total population size. Leave blank for large populations.

Advanced Power Analysis: Determine sample sizes needed to detect meaningful differences between groups.

Effect Size (Cohen's d)Expected effect size: Small (0.2), Medium (0.5), Large (0.8)

Statistical PowerProbability of detecting the effect if it exists.

Significance Level (α)Maximum acceptable Type I error rate.

Test TypeDirection of expected difference.

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