Sample Size Calculator
Enter your confidence level, margin of error, and (optionally) your total population size to calculate the minimum sample size for your questionnaire, survey, or research study.
Save your student profile to track computations, past questions & GPA targets.
Recommended sample size
385 respondents
Formula: n₀ = (Z² × p × (1−p)) / e² using Z = 1.96 for 95% confidence
How It Works
This tool uses Cochran's formula for sample size: n₀ = (Z² × p × (1−p)) / e², where Z is the z-score for your chosen confidence level (90% → 1.645, 95% → 1.96, 99% → 2.576), p is your expected proportion (50% is the most conservative default, since it produces the largest required sample), and e is your margin of error. If you enter a known population size, the tool applies the finite population correction n = n₀ / (1 + (n₀−1)/N) to give a smaller, more precise sample size — useful when your population (e.g. all 400-level students in a department) is small enough that it matters.
MyDelsu is an independent student platform and is not affiliated with DELSU administration. This tool is provided for guidance only — always verify results against your official transcript, result slip, or academic regulations.
This calculator gives a statistically common starting point, not a guarantee your study design is correct — always confirm your sampling methodology with your supervisor or a statistics/research-methods text.
Frequently Asked Questions
What does 'confidence level' mean?+
Confidence level is how sure you can be that your sample's results reflect the true population if you repeated the survey many times. 95% confidence is the most commonly used level in student research — it means that, in the long run, about 95 out of 100 samples drawn this way would produce results within your margin of error of the true population value.
What does 'margin of error' mean?+
Margin of error (also called the confidence interval) is how much your sample results might differ from the true population value, expressed as a percentage. A 5% margin of error means your result could be off by up to ±5 percentage points. A smaller margin of error requires a larger sample size.
Why does the expected proportion default to 50%?+
50% is used when you don't have prior data on how your population is likely to split on the variable you're studying, because p × (1−p) is largest — and therefore the required sample size is largest — when p = 50%. If you have a reasonable estimate from prior research (e.g. 'about 30% of students own a car'), entering it will usually give you a smaller, still-valid sample size.
Is Cochran's formula the only valid way to determine sample size?+
No. Cochran's formula is one common, well-established approach for estimating a sample size for proportions in a survey-style study, but it is not universally correct for every research design. Studies using different statistical tests (e.g. comparing group means, regression analysis) or non-probability sampling may need a different sample-size approach — check with your supervisor or a statistics reference for your specific methodology.
Do I need to know my exact population size?+
No — leave population size blank if your population is unknown or very large (e.g. 'all Nigerian university students'). The tool will use the standard infinite-population formula. Only enter a population size if you know it and it's relatively small (e.g. the number of students in one department or one class).
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