CalcVind

Sample Size Calculator

How many people to survey for reliable results

Survey Details

%

Use 50% if you're not sure: it gives the safest (largest) answer.

%

Leave at 0 for a very large or unknown population.

Sample Size Needed

385People to survey
1.95996
z-score
385
For an unlimited population

Working

  1. n₀ = z² × p(1 − p) ÷ E² = 1.95996² × 0.5 × 0.5 ÷ 0.05² = 384.14588
  2. Round up: 385
  1. 1
    Choose a confidence level
    95% is the usual choice
  2. 2
    Set the margin of error
    And the population, if known
  3. 3
    Get your sample size
    Rounded up to whole people

How is sample size calculated?

For a proportion (like the share of people who agree), the required sample depends on the z-score for your confidence level and the margin of error you'll accept:

n₀ = z² × p(1 − p) ÷ E²

Finite population: n = n₀ ÷ (1 + (n₀ − 1) ÷ N)

95% confidence → z = 1.96

Why population size matters so little

For large populations, the sample you need barely changes: about 385 responses give ±5% at 95% confidence whether the population is 1 lakh or 100 crore. Population size only makes a real difference when it is small, say a few thousand.

Response rates

The result is the number of completed responses. If you expect only 1 in 5 people to reply, contact five times as many.

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Frequently asked questions

What sample size do I need for a survey?

For ±5% margin of error at 95% confidence, about 385 responses from a large population. A small population needs fewer: 278 for a population of 1,000.

What does 95% confidence mean?

If you repeated the survey many times, about 95 out of 100 results would land within the margin of error of the true value.

Why use 50% for the proportion?

p(1 − p) is largest at 50%, so it gives the biggest sample size. It is the safe choice when you don't know the answer in advance.

Last reviewed: October 2026