Sample Size Calculator (Surveys)
By Santaji GadepatilinUpdated October 27, 2026
10,000
calculated
calculated
Type in any field to change it. Press × on a value to calculate that field instead.
How to use this calculator
Choose the confidence level, set the margin of error and the population size. Leave the expected proportion at 50% unless you have a prior estimate. Round the result up.
Formulas
n₀ = z² p(1 − p) ÷ E² n = n₀ ÷ (1 + (n₀ − 1) ÷ N)
Worked example
95% confidence, ±5%, p = 50%, population 10,000:
- n₀ = 1.96² × 0.25 ÷ 0.0025 = 384.1 → 385
- With the population correction: 370 responses
Typical sample sizes (large population, 95%)
| Margin of error | Sample size |
|---|---|
| ±10% | 97 |
| ±5% | 385 |
| ±3% | 1068 |
| ±2% | 2401 |
| ±1% | 9604 |
Account for non-responses: if you expect a 20% response rate, invite five times as many people.
Frequently asked questions
How many people do I need to survey?
For a large population, 95% confidence and ±5% margin, about 385 responses. For ±3%, about 1,068.
Why use 50% for the proportion?
It gives the largest (safest) sample size when you don't know the expected result.
Does population size matter much?
Only for small populations. Above about 20,000, the required sample barely changes.