Survey Sample Size Calculator
Find out how many respondents you need for your survey. Calculate the sample size required to achieve a desired margin of error for proportions or means.
Sample Size Calculator for Surveys
Calculate required sample sizes for surveys and experiments
±5.0%
Use 0.5 for maximum sample size
About Sample Size Calculation
Proportion: Uses Cochran's formula for estimating population proportions (e.g., survey responses, approval ratings).
Mean: Calculates sample size for estimating a population mean with specified precision.
Compare Groups: Determines sample size for detecting differences between two groups (two-sample t-test).
How the Sample Size Calculator Works
Select whether you're estimating a proportion (percentage) or a mean (average). For proportions, enter your expected proportion (use 0.5 if unknown for maximum sample size). For means, enter the estimated standard deviation.
Input your desired confidence level (typically 95%) and margin of error (precision). The margin of error is the half-width of your confidence interval - how close you want your estimate to be to the true value. Enter population size if known for finite population correction.
The calculator uses the appropriate formula: for proportions n = (Z² × p × (1-p)) / E², for means n = (Z² × σ²) / E². Results adjust for finite populations when specified. The required sample size displays with explanation of what it achieves.
When You'd Actually Use This
Political polling design
Determine how many voters to survey for ±3% margin of error at 95% confidence. Balance precision with budget constraints for election polling.
Customer satisfaction surveys
Calculate respondents needed to estimate satisfaction rate within 5%. Ensure your survey results reliably represent the entire customer base.
Market research studies
Plan sample size for product preference studies. Determine how many consumers to interview to make reliable claims about market preferences.
Employee engagement surveys
Find how many employees must respond to get accurate engagement scores. Account for expected response rate when distributing surveys.
Public health surveys
Calculate sample size for prevalence studies. Estimate disease prevalence or health behavior rates with specified precision for public health planning.
Academic research projects
Justify sample size in research proposals. Show reviewers your survey will produce estimates with acceptable precision for your research questions.
What to Know Before Using
Margin of error is half the confidence interval width.A 5% margin of error means your estimate is within ±5% of the true value. Smaller margins require larger samples.
95% confidence is standard but not mandatory.Higher confidence (99%) needs larger samples. Lower confidence (90%) needs fewer. Match confidence level to your decision's importance.
Use 0.5 for proportions when uncertain.p = 0.5 gives the maximum (most conservative) sample size. If you know the proportion is around 0.1 or 0.9, use that for smaller samples.
Finite population correction reduces sample size.When sampling a large fraction of a small population, you need fewer responses. The correction matters when n/N > 5%.
Pro tip: Always inflate your calculated sample size for expected non-response. If you need 400 responses and expect 40% response rate, send 400/0.40 = 1000 invitations.
Common Questions
Why does 50% give the largest sample?
The formula includes p × (1-p), which is maximized at p = 0.5. This represents maximum uncertainty - equal chance of either outcome.
How does population size affect sample size?
For large populations (>100,000), it barely matters. For smaller populations, you need proportionally more. Sampling 100 from 200 is very different than 100 from 1,000,000.
What's a typical margin of error?
Political polls use ±3%. Market research often accepts ±5%. Internal surveys might use ±7-10%. Tighter margins cost more in sample size.
Does this work for stratified sampling?
This calculates total sample size. For stratified sampling, allocate this total across strata proportionally or optimally based on stratum variance.
What if my sample is smaller than calculated?
Your margin of error will be larger than planned. You can calculate the actual margin achieved with your obtained sample size.
How do I estimate standard deviation for means?
Use pilot data, previous studies, or rule of thumb: SD ≈ range/4. If unsure, run a small pilot study to estimate variability before the main survey.
Is this for hypothesis testing?
No, this is for estimation (confidence intervals). For hypothesis testing power calculations, use a statistical power calculator instead.
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