Sample Size Calculator

Use our free sample size calculator to find the minimum sample size required for your survey or experiment. Supports proportions and means.

Math

Type

Confidence level (%)

Margin of error

Estimated proportion (p)

Estimated std dev (σ)

Formula

Calculate the minimum sample size needed to estimate a population proportion or mean with a given confidence level and margin of error. Always rounds up.

n = z² × p × (1-p) / E² (proportion), n = z² × σ² / E² (mean)

Percentage: The percentage value you want to apply

Number: The original number or value

Result: The calculated result

How It Works

1Select proportion or mean.
2Enter the confidence level (e.g., 95).
3Enter the desired margin of error.
4Enter estimated p (for proportion) or σ (for mean).
5Click Calculate.

Examples

95% CI, E=0.05, p=0.5

1.z=1.96
2.n = 1.96²×0.5×0.5/0.05² = 384.16
3.Minimum n = 385

Result: 385

95% CI, E=3, σ=15

1.z=1.96
2.n = 1.96²×15²/3² = 96.04
3.Minimum n = 97

Result: 97

Frequently Asked Questions

The minimum number of observations needed for reliable results.

p=0.5 gives the most conservative (largest) sample size for proportions.

The maximum acceptable difference between sample and population.

Yes, higher confidence requires a larger sample size.

Yes, you need at least the calculated minimum, so always round up.

Related Calculators

Confidence Interval Calculator Z Score Calculator Normal Distribution Calculator Mean Calculator Percentage Calculator Basic Calculator

CalculateMe Team

Last updated: 2026-07-14

Sample Size Calculator

Formula

How It Works

Examples

95% CI, E=0.05, p=0.5

95% CI, E=3, σ=15

Frequently Asked Questions

What is sample size?

Why use p=0.5?

What is margin of error?

Higher confidence = larger n?

Always round up?

Related Calculators

Sample Size Calculator

Formula

How It Works

Examples

95% CI, E=0.05, p=0.5

95% CI, E=3, σ=15

Frequently Asked Questions

What is sample size?

Why use p=0.5?

What is margin of error?

Higher confidence = larger n?

Always round up?

Related Calculators