Sample Size Calculator

Sample Size Determination in Clinical Studies book cover

Book & Calculator Overview

This calculator is based on the practical formulas from "Sample Size Determination in Clinical Studies: A Practical Guide (ISBN 978-81-8487-807-3)" by K.V.S. Sarma and V. Sai Sarada. It brings the book’s guidance online so researchers can quickly estimate sample sizes for proportions, means, comparing groups, paired comparisons, diagnostic accuracy, correlation studies, and survival analysis.

The book itself focuses on clinical research sample size planning, offering detailed explanations of assumptions and formula choices. The calculator simplifies the process by letting you enter study parameters and see the required sample sizes instantly.

Statistics Correspondence

Dr K. V. S. Sarma
Statistics Consultant -- Hyderabad,Telangana,India.
Former Professor of Statistics Sri Venkateswara University, Tirupathi.
Former Biostatistician Sri Venkateswara Institute of Medical Sciences
Tirupathi,AndhraPradesh,India.

E-mail: smskvs@gmail.com

Dr. V. Sai Sarada
Biostatistician
Department of Research Labs
Asian Health Care Foundation, AIG Hospitals
Hyderabad, Telangana, India.

E-mail: saisaradav@gmail.com

Website Correspondence

Abhyuday Suraparaju
Software Developer
Specializations: Python Programming, AI/ML, Data Science

LinkedIn: www.linkedin.com/in/abhyuday-suraparaju E-mail: abhyudaysuraparaju@gmail.com

Inputs

Anticipated Proportion (p)

Margin of error (d%)

Confidence Level (%): 95%

Population size (N)

Attrition (%): 5%

Purpose

Applicable for binary outcomes only. Useful to find the minimum sample size (n) with desired precision d, confidence level 100(1-α)% when the objective is to estimate (describe) a population proportion. The chief input is the anticipated proportion. The calculator gives n assuming infinite population. Adjustments can be made to account for finite population size as well as attrition (coverage for non-response).

Results

Sample Size

Adjusted sample size for finite population

Interpretation

Waiting for inputs...

Formulas

$$ n = \frac{p(1-p)Z^2_{1-\alpha/2}}{d^2} $$

$$ n_{adj} = \frac{nN}{n + (N - 1)} $$

References

1. K.V.S.Sarma and V. Sai Sarada (2026), Sample Size Determination in Clinical Studies - A Practical Guide, Narosa Publishing House, New Delhi.

2. Chow S, Shao J, Wang H. (2008), Sample Size Calculations in Clinical Research. 2nd Ed. Chapman & Hall/CRC Biostatistics Series.

3. Cochran WG (1977), Sampling techniques (3rd ed.). New York: John Wiley & Sons; 1977.

Inputs

Anticipated standard deviation (s)

Confidence Level (%): 95%

Absolute Margin of error (units)

Population size (N)

Attrition (%): 5%

Purpose

Applicable for measured outcomes only. Useful to find the minimum sample size (n) with desired precision d, confidence level 100(1-α)% when the objective is to estimate population mean. The chief input is the anticipated standard deviation of the population characteristic. The calculator gives n assuming infinite population. Adjustments can be made to account for finite population size as well as attrition.

Results

Sample Size

Adjusted sample size for finite population

Interpretation

Waiting for inputs...

Formulas

$$ n = \frac{Z^2_{1-\alpha/2} s^2}{d^2} $$

$$ n_{adj} = \frac{nN}{n + (N - 1)} $$

References

1. K.V.S.Sarma and V. Sai Sarada (2026), Sample Size Determination in Clinical Studies - A Practical Guide, Narosa Publishing House, New Delhi.

2. Chow S, Shao J, Wang H. (2008), Sample Size Calculations in Clinical Research. 2nd Ed. Chapman & Hall/CRC Biostatistics Series.

3. Cochran WG (1977), Sampling techniques (3rd ed.). New York: John Wiley & Sons; 1977.