F-Test Calculator
Compare two variances with F, df and the p-value.
Enter your values
ⓘ Live results
Results
- F statistic
- 2.25
- p-value (two-tailed)
- 0.09871
- Verdict
- Marginal (10% level)
- Degrees of freedom
- 19, 17
- Variance 1
- 144
- Variance 2
- 64
- Equal-variance assumption
- Reasonable — variances are similar
Quick answer
The F-test compares two variances as a ratio: F = larger variance ÷ smaller variance, tested against the F distribution.
F = s₁² ÷ s₂²
How to use the F-Test Calculator
- 1Enter each sample's standard deviation and size.
- 2The calculator always puts the larger variance on top.
- 3Use the verdict to decide between the pooled and Welch versions of the t-test.
Worked example
Using the values the calculator loads with:
Inputs
- Sample 1 SD12
- Sample 1 size20
- Sample 2 SD8
- Sample 2 size18
Results
- F statistic2.25
- p-value (two-tailed)0.09871
- VerdictMarginal (10% level)
- Degrees of freedom19, 17
- Variance 1144
- Variance 264
- Equal-variance assumptionReasonable — variances are similar
Frequently asked questions
Is the F-test sensitive to non-normality?
Very. If your data are skewed, prefer Levene's or Brown-Forsythe test, or just default to Welch's t-test.
Do I even need this test?
Often not — Welch's t-test handles unequal variances automatically, so many statisticians skip the pre-test entirely.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.