Margin of Error Calculator
The ± figure behind any poll or survey result.
Enter your values
Enter the sample size you are working with.
Enter the observed percentage in %.
Choose one of: 90%, 95%, 99%.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Margin of error
- ± 3.1 percentage points
- Confidence interval
- 48.9% to 55.1%
- Is a 50% result inside the interval?
- Yes — result is a statistical tie
Quick answer
Margin of error is z × √(p(1−p)/n) — the range within which the true population value likely falls.
MOE = z·√(p(1−p) ÷ n)
At a glance
| What it does | The ± figure behind any poll or survey result. |
|---|---|
| Category | Statistics |
| Inputs needed | Sample size, Observed percentage, Confidence level |
| Main output | Margin of error |
| Formula | MOE = z·√(p(1−p) ÷ n) |
| Cost | Free — no sign-up, no download |
How to use the Margin of Error Calculator
- 1Enter your sample size.
- 2Enter the percentage you observed.
- 3Pick the confidence level.
Inputs explained
- Sample size
- Enter the sample size you are working with.
- Observed percentage(%)
- Enter the observed percentage in %.
- Confidence level
- Choose one of: 90%, 95%, 99%.
Worked example
Using the values the calculator loads with:
Inputs
- Sample size1000
- Observed percentage52 %
- Confidence level95%
Results
- Margin of error± 3.1 percentage points
- Confidence interval48.9% to 55.1%
- Is a 50% result inside the interval?Yes — result is a statistical tie
Frequently asked questions
Why do polls say ±3?
That is the margin at 95% confidence for a sample of about 1,067 — the industry's standard cost-accuracy compromise.
Does margin of error cover bias?
No. It only measures sampling randomness. Non-response and bad question wording add error it cannot detect.
What do I need to enter into the Margin of Error Calculator?
Just 3 values: sample size, observed percentage, confidence level. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Margin of Error Calculator work out the answer?
Margin of error is z × √(p(1−p)/n) — the range within which the true population value likely falls. It applies the formula MOE = z·√(p(1−p) ÷ n) and shows the working so you can check each step by hand.
Is the Margin of Error Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.