# How to use Margin of Error Calculator

Margin of Error Calculator estimates how wide a survey percentage might swing
before you field the study. Use it when you are choosing a sample size and want
a ± range at a confidence level you pick. In this article you will learn how to
enter sample size and settings, then read the margin of error.

The tool is at form.ms/tools/margin-of-error-calculator
[https://form.ms/tools/margin-of-error-calculator].


1. OPEN THE CALCULATOR

Go to the Margin of Error Calculator
[https://form.ms/tools/margin-of-error-calculator]. Margin of error is about ±
percentage points around your estimate.




2. ENTER SAMPLE SIZE AND SETTINGS

Type Sample size (n) as the completes you expect, not invitations sent. Leave
Expected proportion at 50% when you are unsure. That gives the widest (safest)
margin. Pick 90%, 95%, or 99% confidence. Population size is optional when you
sample a large share of a known group.


3. READ THE ± MARGIN

The page shows the half-width in percentage points. Use it to check whether your
planned n is precise enough before you launch.

After you have real yes/success counts, use the Confidence Interval Calculator
[https://formms.help.center/article/1031-how-to-use-confidence-interval-calculator].
That tool uses Wilson intervals on actual results, not a planning formula.