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Conversion Rate and A/B Test Calculator

Work out a conversion rate, or check whether an A/B test result is statistically significant.

Result

Enter your values and select Calculate to see the result.

Runs in your browser — nothing you enter is sent to a server.

How the Conversion Rate and A/B Test Calculator works

Conversion rate is the share of visitors who do what you want — buy, sign up or download. Enter visitors and conversions to get the rate.

A/B test compares two versions. Enter visitors and conversions for A and B; a two-proportion z-test tells you how likely it is that a difference this large is just chance (the p-value). If the p-value is below 5%, the result is significant at 95% confidence.

Formulas

Conversion rate

rate = conversions ÷ visitors × 100%

z-test

z = (p₂ − p₁) ÷ √(p(1 − p)(1/n₁ + 1/n₂))

p is the pooled rate of both variants; n₁ and n₂ are their visitors.

Examples

A landing page

50 sign-ups from 2,000 visitors is a 2.5% conversion rate.

An A/B test

10,000 visitors each: A converts 200 (2%), B converts 260 (2.6%) — a 30% relative lift with a p-value of about 0.005, so B wins at 95% confidence. With only 500 visitors each, 10 vs 13 conversions isn't significant.

Frequently asked questions

When can I stop a test?

Decide the sample size in advance and run for at least a full week or business cycle. Stopping as soon as the result looks significant makes false winners much more likely.

What confidence level should I use?

95% is the usual choice. Use 99% for costly or hard-to-reverse changes.

Significant means important?

No — only that the difference probably isn't chance. A tiny lift can be significant but not worth the effort.

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