Clinical Research Sample Size Calculator
Determine appropriate sample sizes for your clinical studies
Select Study Type:
Two Sample Comparison
One Sample Test
Proportion Comparison
Survival Analysis
Effect Size (Cohen's d)
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Standardized difference between groups. Small: 0.2, Medium: 0.5, Large: 0.8
Power (1-β)
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Probability of detecting a true effect. Common values: 0.8 (80%) or 0.9 (90%)
80% (0.8)
90% (0.9)
95% (0.95)
Significance Level (α)
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Probability of Type I error. Common value: 0.05 (5%)
5% (0.05)
1% (0.01)
10% (0.10)
Test Type
Two-tailed
One-tailed
Allocation Ratio (Control:Treatment)
?
Ratio of control to treatment group sizes. 1:1 means equal groups
1:1 (Equal groups)
2:1 (2 control : 1 treatment)
1:2 (1 control : 2 treatment)
Effect Size (Cohen's d)
Power (1-β)
80% (0.8)
90% (0.9)
95% (0.95)
Significance Level (α)
5% (0.05)
1% (0.01)
10% (0.10)
Test Type
Two-tailed
One-tailed
Control Group Proportion (p1)
Treatment Group Proportion (p2)
Power (1-β)
80% (0.8)
90% (0.9)
95% (0.95)
Significance Level (α)
5% (0.05)
1% (0.01)
10% (0.10)
Allocation Ratio (Control:Treatment)
1:1 (Equal groups)
2:1 (2 control : 1 treatment)
1:2 (1 control : 2 treatment)
Control Group Median Survival (months)
Treatment Group Median Survival (months)
Accrual Period (months)
Follow-up Period (months)
Power (1-β)
80% (0.8)
90% (0.9)
95% (0.95)
Significance Level (α)
5% (0.05)
1% (0.01)
10% (0.10)
Calculate Sample Size
Required Sample Size Per Group
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Total Sample Size:
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Assumptions & Notes