# What A/B test calculator can I use to calculate the minimum same size for uneven split between control and treatment groups?

I have only come across A/B test calculators that give the minimum sample size per variation for 50-50 split between control and treatment.

I am running an A/B test for conversion rates with a 80/20 split between control and treatment. I need to calculate the minimum sample size needed for statistical significance. Can anyone point me to the calculator that does so for uneven split between control and treatment?

Example calculator i have found so far :'https://www.evanmiller.org/ab-testing/sample-size.html' . This calculator is only for 50-50 split.

• Please describe what about the problem made a hypothesis test (test for existence of a signal) appropriate, as opposed to estimating the magnitude of an effect (with sample size chosen to achieve a certain precision in the estimate, i.e., margin of error). – Frank Harrell Jun 30 '19 at 12:40

From the point of view of the 'power' of the test, the most efficient design is to have equal sample sizes in A and B, so it is customary for software programs and online calculators to assume that $$n_1 = n_2$$ and then give you the number required in each group to achieve a given power for detecting a given difference in means.
If you could say what kind of test your will do, it might be possible to give a formula based on both $$n_1$$ and $$n_2.$$ If not a formula, then a simulation method.