Survey Sample Size Calculator
Determine exactly how many survey responses you need for statistically valid results. Set your confidence level, margin of error, and get instant calculations with outreach recommendations.
Sample Size Calculator
Calculate Your Survey Sample Size
Determine exactly how many responses you need for statistically valid results
The Sample Size Formula Explained
Finite Population Correction
For smaller populations (under 50,000), apply this correction to reduce the required sample size:
Where N is your total population size. This adjustment recognizes that sampling a larger percentage of a small population provides more information.
Confidence Levels & Z-Scores
The Z-score represents how many standard deviations from the mean your results need to be. Higher confidence requires higher Z-scores, which increases sample size requirements.
Quick pulse surveys, internal research, early-stage exploration
NPS, CSAT, customer satisfaction, most business surveys
Regulatory, medical research, major strategic decisions
Quick Reference: Sample Sizes by Population
Find your population size and read across for the required sample at different precision levels. Notice how larger populations converge toward the same sample size.
| Population | 95% / ±5% | 95% / ±3% | 99% / ±5% |
|---|---|---|---|
| 100 | 80 | 92 | 87 |
| 500 | 217 | 341 | 286 |
| 1,000 | 278 | 517 | 400 |
| 5,000 | 357 | 880 | 586 |
| 10,000 | 370 | 965 | 623 |
| 50,000 | 381 | 1,045 | 655 |
| 100,000+ | 384 | 1,068 | 664 |
Key Insight: The "Magic Number"
For populations over 100,000, the required sample size converges to 384 responses (at 95% confidence, ±5% margin). This is why 400 responses is considered the gold standard for most business surveys - it works regardless of whether your population is 100,000 or 100 million.
Typical Survey Response Rates
Knowing expected response rates helps you plan outreach volume. Divide your required sample size by the response rate to determine how many surveys to send.
Employee Surveys
Internal company surveys with management support and clear communication
Exit Surveys
Offboarding and churn surveys with relevant timing
Transactional (NPS)
Quick 1-2 question surveys triggered by specific events
In-App Feedback
Contextual micro-surveys within product experiences
Customer Surveys
Post-purchase and general satisfaction surveys
Market Research
Panel surveys and cold outreach to new contacts
Example Calculation
Frequently Asked Questions
How do I calculate survey sample size?
Sample size is calculated using the formula: n = (z² × p × (1-p)) / e², where z is the z-score for your confidence level (1.96 for 95%), p is the expected proportion (use 0.5 if unknown), and e is your margin of error as a decimal. For finite populations, apply the correction: n_adjusted = n / (1 + (n-1)/N) where N is population size.
What sample size do I need for a 95% confidence level?
For a 95% confidence level with ±5% margin of error, you need 385 responses for large/unknown populations. For smaller populations: 1,000 people needs 278 responses, 500 people needs 217 responses, and 100 people needs 80 responses. The required sample decreases as population gets smaller.
What is a good sample size for a survey?
A "good" sample size depends on your goals. For most business surveys, 385-400 responses at 95% confidence with ±5% margin of error is the industry standard. For exploratory research, 100-200 may suffice. For segment analysis, multiply by the number of segments you want to analyze separately (e.g., 385 × 3 segments = 1,155).
Does population size matter for sample size calculation?
Population size only matters for smaller populations (under 50,000). For populations over 50,000, the required sample size is essentially the same whether you're surveying 50,000 or 50 million people. A sample of 385 can accurately represent both. Apply the finite population correction only when surveying more than 5% of your total population.
What is margin of error and how does it affect sample size?
Margin of error defines the range within which the true population value likely falls. If your survey shows 70% satisfaction with ±5% margin, the true value is between 65-75%. Smaller margins require exponentially larger samples: halving the margin (10% → 5%) requires quadrupling the sample size (96 → 385 responses).
What confidence level should I use for my survey?
95% confidence is the standard for most business surveys - it means if you ran the survey 100 times, 95 would fall within your margin of error. Use 90% for quick exploratory research, 95% for customer satisfaction and NPS surveys, and 99% for high-stakes decisions with significant financial or safety implications.
How many people should I survey to reach my sample size target?
Divide your required sample size by your expected response rate. For example, if you need 400 responses and expect 10% response rate: 400 ÷ 0.10 = 4,000 surveys to send. Response rates vary: customer surveys average 10-20%, employee surveys 50-70%, cold outreach 2-5%.
Is 100 survey responses enough for valid results?
100 responses can provide directional insights but has limitations. At 95% confidence, 100 responses gives ±10% margin of error (twice the standard ±5%). It's adequate for pulse surveys, small populations, or early-stage research. For decisions with significant consequences, aim for 385+ responses.
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