Super practical AB Testing Calculators
https://abtestguide.com/calc/
https://conversionxl.com/ab-test-calculator/
http://www.abtestcalculator.com/
https://www.evanmiller.org/ab-testing/
Sample Size Calculator
https://www.abtasty.com/sample-size-calculator/
https://unbounce.com/ab-test-duration-calculator/