Statistics

A/B Test Sample Size Calculator

n per variant from baseline, MDE, confidence, power. Free browser tool on MyCalcsWorld — transparent math, no signup.

Runs in your browserFreeNo signupEducational estimates — not professional advice

Guide & FAQ ↓When to use Example Mistakes Formula

Results

n per variant

3,528

Total (2 variants)

7,056

Note: Equal-allocation two-proportion approximation.

Formula / how it works

n ≈ 2(zα/2 + zβ)² × p(1−p) / δ² with δ = MDE in absolute proportion. Defaults 95% / 80% power.

Detailed guide

What it is, how to use it, how to read the numbers, common mistakes, a worked example, formulas, and FAQs.

What this calculator is

A/B Test Sample Size Calculator on MyCalcsWorld helps you n per variant from baseline, MDE, confidence, power. Enter the labeled fields, read the emphasized outputs, and use related tools when you want a second angle on the same decision. Defaults are realistic demos — replace them with your own numbers. Results are educational planning aids — not licensed financial, tax, medical, legal, or engineering advice. Cross-check critical numbers with primary sources or qualified professionals when stakes are high.

When to use / who it helps

Quickly checking a/b test sample size numbers without a spreadsheet.
Comparing scenarios by changing one input at a time.
Learning the underlying formula with a worked example.
Sharing a transparent estimate with a teammate, client, or classmate.
Use the A/B Test Sample Size Calculator to validate homework summaries or exploratory stats on small samples.

How to use

Steps

Open the calculator and review the default demo values.
Replace defaults with your own figures in the labeled fields.
Read the primary emphasized results and any disclaimer notes.
Optional: tweak one input to see sensitivity.
Follow related links if you need a companion calculation.
Open the A/B Test Sample Size Calculator on MyCalcsWorld and skim the labeled fields before you type.

How to interpret results

Emphasized rows are the headline outputs for most users.
Secondary rows provide unit, margin, or context checks.
Disclaimers flag educational or illustrative limits — take them seriously.
On the A/B Test Sample Size Calculator, read the large primary result first, then secondary totals, then any chart or table.
Each result is driven only by the labeled inputs (Baseline conversion (%), Minimum detectable effect (pp), Confidence (%), Power (%)); anything not on the form (fees, holidays, clinical adjustments) is outside this estimate.

Common mistakes & gotchas

Mixing units (percent vs decimal, hours vs minutes, miles vs km).
Treating illustrative defaults or tables as official policy or diagnoses.
Ignoring fees, taxes, waste, or utilization that change the real answer.
Using the output as a substitute for professional advice on regulated topics.
Using population variance when the homework wants the sample formula (or reverse).

Worked example

Worked example — 10% baseline, 2pp MDE

Use 95/80 z values.
Compute n per arm.
Double for two variants.
Open the A/B Test Sample Size Calculator (ab test sample size) and note the starting defaults (baseline conversion 10 %, minimum detectable effect 2 pp, confidence 95 %, power 80 %). These are demo numbers — not recommendations.

Result: With defaults (baseline conversion 10 %, minimum detectable effect 2 pp, confidence 95 %, power 80 %), the A/B Test Sample Size Calculator shows: n per variant 3,528; Total (2 variants) 7,056. Re-run with your own numbers for a personalized estimate — illustrative only, not professional advice.

Want these demo numbers in the form? Tap Try example above the Calculate button.

How to calculate / formula

n ≈ 2(zα/2 + zβ)² × p(1−p) / δ² with δ = MDE in absolute proportion. Defaults 95% / 80% power.

Frequently asked questions

What does the a/b test sample size calculator do?

It computes the labeled outputs from your inputs using the formula note on the page — instantly in the browser.

Are results professional advice?

No. MyCalcsWorld provides educational estimates. Confirm regulated, medical, or financial decisions with qualified professionals.

Can I change units or defaults?

Yes — edit every field. Mode selectors appear when a tool supports alternate inputs.

Does this work worldwide?

Math is unit-labeled and currency-aware where marked. Always match local rates, limits, and conventions.

How is a/b test sample size different from related tools?

Related links cover sibling workflows. Use the calculator whose inputs match your question.

Is my data stored?

Calculations run in your browser session for this page — treat outputs as something you can screenshot or copy, not a saved transcript.

What does the A/B Test Sample Size Calculator on MyCalcsWorld actually compute?

Estimate users needed per variant from baseline conversion %, absolute MDE, confidence, and power. You enter Baseline conversion (%), Minimum detectable effect (pp), Confidence (%), Power (%), and the result panel updates in your browser — free, no signup. Below the form you will find when-to-use tips, common mistakes, a worked example, formula notes, and FAQs for this tool.

How do I use the A/B Test Sample Size Calculator step by step?

Start from the defaults (baseline conversion 10 %, minimum detectable effect 2 pp, confidence 95 %, power 80 %) or type your own values into Baseline conversion (%), Minimum detectable effect (pp), Confidence (%), Power (%). Watch the live results (and any chart or table). Then scroll to interpretation tips and the worked example before you rely on the figure for a real decision. Related Statistics tools sit in the sidebar and “You might also like” section.

Disclaimer: Results are estimates for educational purposes and are not a substitute for professional financial, medical, legal, or tax advice. FX and commodity quotes are delayed reference data. Read more

Questions about this tool? Contact MyCalcsWorld · mycalcsworldcontact@gmail.com

Statistics

A/B Test Sample Size Calculator

Inputs

Saved scenarios