A free sample size calculator for medical and health research, made by UPMED for doctors, postgraduate trainees and researchers in Pakistan. It covers every calculator of the WHO manual by Lwanga and Lemeshow, plus means, correlation and diagnostic accuracy, and shows every step of the arithmetic so you can copy the working into your synopsis, proposal or thesis.
Choose the calculator that matches your study design, enter the values from a published study or a pilot (for example the expected prevalence, standard deviation or odds ratio), and set the confidence level, power and precision. The sample size appears at once, with the formula, the values used and each step. Add a finite population correction, a design effect or a non-response rate if you need them, then download the calculation as a PDF, JPG or text file.
Yes. Every calculator, the step-by-step working and the PDF, JPG and text downloads are free, with no sign-up.
The WHO manual by Lwanga and Lemeshow, Sample size determination in health studies: a practical manual (Geneva: World Health Organization; 1991), for proportions, odds ratios, relative risks, incidence rates and lot quality assurance. Means, correlation (Fisher's z) and diagnostic accuracy (Buderer's method) use the standard formulas cited on each calculator.
For a prevalence or cross-sectional study, use a single proportion. For comparing two groups, use two proportions or two means. For a case-control study, use the odds ratio calculators. For a diagnostic accuracy study, use sensitivity and specificity.
Yes. You can add a finite population correction, a design effect for cluster sampling and a non-response (drop-out) rate. Each adjustment is shown in the working.
Yes. Download the calculation as a plain black-and-white PDF, JPG or text file in Times New Roman 12 pt, with every step of the working and the reference for the formula.
Yes. Install it on your phone or computer from the browser. After it has been opened once with internet, it works offline.
Need help with your research? Chat with UPMED on WhatsApp.