Statistics3 options compared

Sample Size Calculator

Estimates the required sample size for A/B testing to determine if observed performance differences are statistically significant. Users input key parameters such as a baseline conversion rate and the minimum detectable lift they wish to achieve. The tool then calculates the necessary number of visitors per variant, providing a clear understanding of the scale needed for reliable results. It also...

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Editors’ Top PickBased on community votes
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  1. Screenshot of Calculator.net
    02
    Calculator.net
    calculator.net

    This free sample size calculator determines the sample size required to meet a given set of constraints. Also, learn ...

    Open siteView details
  2. Screenshot of TrafficLoopback
    03
    TrafficLoopback
    trafficloopback.com

    A/B test sample size calculator. Enter your baseline conversion rate and minimum detectable lift to see the visitors ...

    Open siteView details

Side by side

Sample Size Calculator options compared

ToolBest forStrengthsLimitations
Omni Calculator
omnicalculator.com
Traditional research studies
  • Uses confidence level, power, and effect size
  • Provides precise population number
  • Requires margin of error and proportion estimate
  • No A/B test duration estimate
Calculator.net
calculator.net
General sample size needs
  • Handles population proportion and size
  • Also calculates margin of error
  • Interface is dense with options
  • No A/B test specific inputs like lift
TrafficLoopback
trafficloopback.com
A/B testing with traffic planning
  • Takes baseline conversion rate and MDE
  • Estimates test duration per variant
  • Includes bandit alternative for fewer impressions
  • Only supports up to 6 variants
  • Bandit estimate is conservative at 40% reduction

Buyer's guide

How to choose a sample size calculator

When picking a sample size calculator, first decide whether you are designing a standard research study or running an live A/B test. For A/B testing, you need a tool that asks for your baseline conversion rate and the smallest lift you care about detecting; those inputs drive the visitor count and test duration. If you are planning a survey or study where you control the sample, look for fields like confidence level, margin of error, and expected proportion. The differences that matter most are the input format (conversion rate vs. margin of error) and whether the tool outputs test duration or bandit trade-offs.

Questions

Sample Size Calculator FAQ

What is the minimum detectable effect and why does it matter?
1-3 sentence answer grounded in the material
How does statistical power affect the sample size needed?
1-3 sentence answer grounded in the material
Can I use these calculators if my population is very small?
1-3 sentence answer grounded in the material
What is the difference between significance level and confidence level?
1-3 sentence answer grounded in the material
How accurate is the test duration estimate from TrafficLoopback?
1-3 sentence answer grounded in the material
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