Sample Size Calculator
Find how many responses your survey needs for the confidence level and margin of error you want, with an adjustment for small populations.
50% if you don't know; it gives the largest, safest sample.
Leave at 0 for a very large population.
Sample size needed
385 responses
- Z-score for this confidence
- 1.96
For 95% confidence and a ±5% margin of error, survey at least 385 people.
How it's worked out
- Unlimited population
z² × p(1 − p) ÷ e² = 1.96² × 0.5 × 0.5 ÷ 0.05²384.1
- This assumes a random sample. Plan for non-responses by inviting more people than the number you need.
The formula
n₀ = z² × p(1 − p) ÷ e² · With a population of N: n = n₀ ÷ (1 + (n₀ − 1) ÷ N)
Worked example
At 95% confidence (z = 1.96), p = 50% and e = 5%: 1.96² × 0.25 ÷ 0.0025 = 384.2, so 385 responses. From a population of 1,000, 278 are enough.
Questions people ask
How many people do I need to survey?
For 95% confidence and a ±5% margin of error, about 385 from a large population.
Why use 50% as the expected proportion?
It gives the largest sample, so it's safe when you don't know what to expect.
What if my population is small?
Enter its size: the finite population correction lowers the number. From 1,000 people you need about 278.
About this calculator
Formula and rules last checked 25 October 2026Written and tested by the CalculatorDex teamReport a problem