Sample Size Calculator
Determine how many responses you need for statistically significant results.
What This Means
You need at least 385 responses to be 95% confident that your results are within ±5% of the true value. This uses the most conservative estimate (50/50 split).
Formula Used
Z = 1.96 (for 95% confidence)
p = 0.5 (expected proportion)
E = 0.05 (margin of error)
n = Z² × p × (1−p) / E²
n = 1.96² × 0.5 × 0.50 / 0.05²
n = 3.8416 × 0.2500 / 0.002500
n = 385
Understanding Sample Size
When conducting a survey or study, you rarely have time to ask every single person in a population. Instead, you ask a sample and use statistics to infer results about the wider group.
The confidence level tells you how sure you can be. A 95% confidence level means that if you repeated the survey 100 times, 95 of those times the true value would fall within your margin of error.
The margin of error is the plus-or-minus range. A 5% margin means your result could be up to 5 percentage points higher or lower than the true value. Smaller margins require larger samples.
If you know your total population size, the finite population correction can reduce the required sample size, because sampling a larger proportion of a small group gives more precise estimates.