10 Best Sample Size Calculator Tools for Founders [2026 Updated]

1. Qualtrics Sample Size Calculator

• Type: Free
• URL: https://www.qualtrics.com/experience-management/research/determine-sample-size/
• Overview: A free online calculator from Qualtrics that estimates the number of survey respondents needed based on confidence level, margin of error, and population size. It is popular with marketers running customer surveys and market research studies.

2. SurveyMonkey Sample Size Calculator

• Type: Free
• URL: https://www.surveymonkey.com/mp/sample-size-calculator/
• Overview: A simple calculator that tells you how many responses you need for statistically meaningful survey results. It lets you enter population size, confidence level, and margin of error, and it fits naturally with SurveyMonkey's survey tools.

3. Calculator.net Sample Size Calculator

• Type: Free
• URL: https://www.calculator.net/sample-size-calculator.html
• Overview: A straightforward calculator that determines the sample size required for a given confidence level and margin of error. It also works in reverse to compute the confidence level or margin of error from an existing sample size.

4. Optimizely A/B Test Sample Size Calculator

• Type: Free
• URL: https://www.optimizely.com/sample-size-calculator/
• Overview: A calculator built for marketers running A/B tests, estimating how many visitors each variation needs. It uses baseline conversion rate, minimum detectable effect, and statistical significance to plan experiments.

5. Evan Miller's Sample Size Calculator

• Type: Free
• URL: https://www.evanmiller.org/ab-testing/sample-size.html
• Overview: A widely referenced calculator for A/B test planning that computes the sample size per variation from baseline conversion rate and minimum detectable effect. It lets users set statistical power and significance level, which makes it favored by experienced experimenters.

6. VWO A/B Test Sample Size Calculator

• Type: Free
• URL: https://vwo.com/tools/ab-test-duration-calculator/
• Overview: A free tool from VWO that estimates how long an A/B test should run based on traffic, conversion rate, and expected uplift. It helps conversion optimization teams plan tests that reach reliable conclusions.

7. Statsig

• Type: Free
• URL: https://www.statsig.com/calculator
• Overview: A free calculator from Statsig that estimates the sample size needed for product and marketing experiments. It uses baseline rate, minimum detectable effect, power, and significance level to plan reliable tests.

8. Raosoft Sample Size Calculator

• Type: Free
• URL: http://www.raosoft.com/samplesize.html
• Overview: A classic web calculator that returns the recommended sample size from margin of error, confidence level, population, and expected response distribution. It is commonly used for customer research and opinion surveys.

9. G*Power

• Type: Free
• URL: https://www.psychologie.hhu.de/arbeitsgruppen/allgemeine-psychologie-und-arbeitspsychologie/gpower
• Overview: A downloadable statistical power analysis program that calculates sample sizes for t-tests, ANOVA, regression, and other tests. It suits advanced market researchers who need rigorous power analysis for complex studies.

10. PASS Sample Size Software (NCSS)

• Type: Paid
• URL: https://www.ncss.com/software/pass/
• Overview: A professional power analysis and sample size software package covering hundreds of statistical procedures and study designs. It is aimed at enterprise research teams and analysts who need validated, documented calculations for large-scale studies.