Grace Ge

Grace Ge

Building systems for better decisions.

Building systems for better decisions.

Decision Systems Toolkit

A/B Test Calculator

Decision Systems Toolkit

A/B Test Calculator

Run statistically sound A/B tests.

Interpret results with confidence.


A lightweight, offline toolkit — no installation, no account.
Download once, open anytime in your browser.


Yours to keep.

Run statistically sound A/B tests.

Interpret results with confidence.


A lightweight, offline toolkit — no installation, no account.
Download once, open anytime in your browser.


Yours to keep.

COMPARE · SIZE · CHECK


Compare means or proportions.
Size your test before you run it.
Check whether it can detect the difference.


Free · Open source · Runs locally

COMPARE · SIZE · CHECK


Compare means or proportions.
Size your test before you run it.
Check whether it can detect the difference.


Free · Open source · Runs locally

Four practical tools for common A/B testing decisions.

Four practical tools for common A/B testing decisions.

What's Included

What's Included

Compare metrics, estimate sample size, and evaluate statistical significance.
Everything you need for common A/B testing decisions in one toolkit.

Compare metrics, estimate sample size, and evaluate statistical significance.
Everything you need for common A/B testing decisions in one toolkit.

01 · Mean Comparison

Compare continuous metrics such as revenue, order value, or time on page.

02 · Proportion Comparison

Compare conversion rates and other binary outcomes.

03 · Sample Size

Estimate how many observations you'll need before running a test.

04 · Statistical Power

Understand whether your experiment has enough power to detect a difference.

Three examples, three different moments where a test goes wrong.

Each one takes a decision that looked settled, and shows where the doubt should have come in — reading the result, sizing the test, or choosing how many places to look.

Example 01 — When “Not Significant” Doesn’t Mean “No Effect”

The moment you read the result.

Example 02 — Was 8 More Sign-Ups a Real Result?

The day you picked the sample size.

Example 03 - Would You Trust the Store That “Worked”?

The number of places you looked before you found it.

Together they cover the three questions worth asking before acting on any test result: Is the difference real? Could this test have seen it? How many did you look at?

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Building systems for better decisions.

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