T-Test vs Z-Test Rule
- Use Z-Test: Sample size n ≥ 30 AND population standard deviation (σ) is KNOWN.
- Use T-Test: Sample size n < 30 OR population standard deviation (σ) is UNKNOWN.
Statistics 8 min read
T-Test vs Z-Test: When to Use Which? (Key Differences)
Learn the differences between Student’s t-test and Z-test in statistics. Master sample size (n > 30) and population standard deviation rules.
Published August 11, 2026
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Basic Math Tools STEM Editorial Team
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Updated: August 11, 2026
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