Free Tools
Calculators

A/B Testing Sample Size Calculator

Find the visitors needed per variant before an experiment can detect the lift you care about.

Run tests in Otter

Required sample size

3,839

per variant

Total for A/B

7,678

for control plus one variant

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Duration Calculator

Turn required sample size into a run-time estimate using daily traffic and number of variants.

Significance Calculator

Check completed control and variant counts with a two-sample conversion-rate test.