Sample Size Calculator for Research Studies
An adequate sample size is one of the first things an ethics committee, guide or journal reviewer checks. ResearchTry's sample size calculator walks you through the decision step by step: you choose your study design, enter values from previous literature or a pilot study, and receive the required sample size together with the formula, calculation steps, assumptions and a ready-to-use justification paragraph.
The calculator covers common designs used in clinical and public health research, including estimation of a proportion or mean, comparison of two proportions or two means, correlation studies, diagnostic accuracy studies and others. Results are rounded up to the next whole participant, and adjustments for expected non-response or dropout can be applied.
Who it is designed for
- Postgraduate students writing a thesis synopsis or protocol
- Researchers preparing an ethics committee submission
- Faculty members guiding student research projects
- Clinicians designing hospital-based observational or interventional studies
Key capabilities and benefits
Guided design selection
A short wizard helps you identify the correct calculation for descriptive, comparative, correlation and diagnostic study designs.
Transparent calculation steps
Each result shows the formula used, the values substituted and the intermediate steps, so you can verify and reproduce the calculation.
Effect size support
Enter means and standard deviations, proportions or correlation coefficients from earlier studies, or derive them from pilot data.
Adjustments
Inflate the calculated size for anticipated dropout or non-response so the final recruited sample remains adequate.
Justification text
A formal paragraph describing the calculation is generated for your synopsis or methodology chapter.
Export
Download the result and steps as a Word, PDF or Excel report for your records or submission.
How it works
- Step 1
Choose your study design
Select the type of study and the primary outcome you plan to measure.
- Step 2
Enter your parameters
Provide confidence level, power and values such as expected proportions or means taken from literature or pilot data.
- Step 3
Get the result
Review the required sample size, calculation steps and justification paragraph, then export them.
Research use cases
- Estimating the prevalence of a condition in a community survey
- Comparing mean outcomes between two treatment groups
- Comparing proportions such as complication rates between two procedures
- Planning a diagnostic accuracy study for sensitivity and specificity
- Justifying the sample size in a thesis synopsis for an ethics committee
Accuracy and limitations
A sample size calculation is only as reliable as the input values. Use estimates from well-conducted, comparable studies, and cite them in your synopsis.
Commonly used defaults are a 95% confidence level and 80% power, but your discipline or guide may require different values.
Complex designs such as cluster sampling, repeated measures or multi-arm trials may need additional design effects or specialist input from a biostatistician.
Always round the final number up and consider practical feasibility, including recruitment time and resources.
Frequently asked questions
Which study designs are supported?
Descriptive studies estimating a proportion or mean, comparative studies of two means or two proportions, correlation studies, diagnostic accuracy studies and other common designs used in clinical research.
Where do I get the values to enter?
From previously published studies similar to yours, or from a small pilot study. The calculator also accepts pilot data to help estimate effect sizes.
Does the calculator show how the result was obtained?
Yes. The formula, substituted values and each calculation step are shown along with the final rounded-up sample size.
Can I add an allowance for dropouts?
Yes. You can apply an expected dropout or non-response percentage, and the adjusted sample size is shown separately.
Can I use the output in my synopsis?
Yes. A formal justification paragraph and a downloadable report are provided. Have your guide review the inputs before submission.
Related ResearchTry tools
- Synopsis PlannerOrganize objectives, methodology, variables, timelines and analysis plans with a guided research synopsis workflow.
- Statistical AnalysisUpload research data, choose suitable statistical tests, and generate structured tables, graphs and interpretations with ResearchTry.
- Literature SearchFind relevant scientific literature across multiple academic databases from one structured research workflow.
Ready to begin?
Open the Sample Size Calculator tool and start your work.