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Sample Size Calculator

While testing may seem daunting or time consuming, it doesn’t have to be. We’ve created this sample size calculator to help determine what percentage of your list should receive the “test” version of your email marketing experiments.

To use the sample size calculator, you’ll need to provide a few pieces of information:

Confidence Level: This is the probability that your sample accurately reflects the attitudes of your population. A confidence level of 95% means the email test result is 95% reliable.

List Size: This is the number of subscribers on your email list.

Acceptable Margin of Error: This expresses the acceptable level of random sampling error in an email’s test results. The smaller the margin of error, the closer you are to having exact results at a given confidence level.


  • 99% confidence level will require a larger sample size than 95% confidence level.
  • As your margin of error decreases, the required sample size increases.