CleanUtils

A/B Test Sample Size Calculator

Estimate visitors per variant from baseline conversion rate, MDE, confidence, and power.

Also useful for: ab test sample size calculator split test sample size conversion test calculator minimum detectable effect calculator A/B Test Sample Size Calculator

A/B Test Sample Size Calculator

Runs in your browser. Inputs are not uploaded.
Input
Results 
Summary: Estimated 31,243 visitors per variant for this A/B test.

Stats
- Per Variant: 31243
- Total: 62486

Issues
- No issues found.

Output
Baseline conversion rate: 5.00%
Minimum detectable effect: 10.0% relative
Target variant rate: 5.50%
Sample size per variant: 31,243
Total two-variant sample: 62,486

A/B Test Sample Size Calculator Example Run

Estimate visitors per variant before launching a test.

Sample inputs
Experiment
Baseline conversion rate: 5
Minimum detectable effect: 10

Statistics
Confidence: 95%
Power: 80%

Generated result
Summary: Estimated 31,243 visitors per variant for this A/B test.

Stats
- Per Variant: 31243
- Total: 62486

Issues
- No issues found.

Output
Baseline conversion rate: 5.00%
Minimum detectable effect: 10.0% relative
Target variant rate: 5.50%
Sample size per variant: 31,243
Total two-variant sample: 62,486

What the A/B Test Sample Size Calculator Checks

  • Baseline conversion rate

    The current conversion rate anchors the sample-size estimate.

  • Relative MDE

    Minimum detectable effect is treated as a relative lift over baseline.

  • Confidence and power

    Common confidence and power settings select the z-values used in the approximation.

  • Per-variant and total sample

    The output shows both one-variant and two-variant sample needs.

  • Planning approximation

    The math is for planning and does not replace a full experiment-design review.

A/B Test Sample Size Calculator Questions

  • Q: Does the A/B test sample size calculator upload my experiment assumptions? A: No. Inputs are processed in your browser, and pasted content is not sent to analytics or a server.
  • Q: What should I paste into the A/B test sample size calculator? A: Enter baseline conversion rate, minimum detectable effect, confidence, and power.
  • Q: What can I copy or download? A: You can copy the estimated sample size per variant and total sample.
  • Q: What does the A/B test sample size calculator not verify? A: It does not handle sequential testing, multiple comparisons, seasonality, allocation imbalance, or non-binomial metrics.

Related Tools

Updates

  • v1.0.0 New 2026-05-17: Initial two-variant sample size estimator with confidence and power controls added.

Use A/B Test Sample Size Calculator with an LLM

Copy the prompt or pass the llms.txt contract link to your assistant.

Prompt 
Use the CleanUtils A/B Test Sample Size Calculator tool for this request.
Tool contract: https://cleanutils.com/business-tools/ab-test-sample-size-calculator/llms.txt

Read the llms.txt contract, ask me for any missing required input, then follow the contract exactly. If the contract includes JavaScript, run `runCleanUtilsTool(userInput)` in a sandboxed JavaScript runtime and return the result with any warnings or errors.
llms.txt https://cleanutils.com/business-tools/ab-test-sample-size-calculator/llms.txt