Enough theory – let’s make this practical. I’ve built a free calculator that does all the math for you. No spreadsheets, no complex formulas, just straightforward answers.

How to use it:

1. Pick your study type – Click either “Descriptive Study” (for baselines and monitoring) or “Impact Evaluation” (for comparing treatment vs control groups)
2. Fill in the numbers – Each field has helpful hints below it. If you’re not sure what to enter, use the default values – they’re the standard settings most M&E practitioners use
3. Hit calculate – You’ll instantly see how many people you need to survey, plus a breakdown of all your inputs so you can double-check everything
4. Read the tips – Below your results, there’s a box with next steps about adjusting for cluster sampling and dropout

The calculator uses the same formulas statisticians use, but without making you understand the math. If you want to save your results, just take a screenshot or write down the number before switching tabs.

Quick tip: Try different scenarios. Change your margin of error from 5% to 10% and watch how much your sample size drops. This helps you see the tradeoffs when you’re tight on budget.