Question 1

How do I calculate sample size?

Accepted Answer

Use Cochran's formula: n₀ = (Z² × p × (1-p)) / E², where Z is the z-score for your confidence level, p is the estimated proportion (usually 0.5), and E is the margin of error. For finite populations, apply the correction factor.

Question 2

What confidence level should I use?

Accepted Answer

95% confidence level is the most common choice. This means if you repeated your survey 100 times, 95 of those surveys would capture the true population value. Use 99% for critical research or 90% for preliminary studies.

Question 3

What is margin of error?

Accepted Answer

The margin of error is the range within which the true population value is expected to fall. A 5% margin of error means your result is accurate to within ±5 percentage points.

Question 4

When should I enter the population size?

Accepted Answer

Enter the population size when your target group is small (under 100,000). For very large or unknown populations, leave it at 0 and the calculator will use the infinite population formula.