Design Better Clinical Trials. Faster.
The all-in-one platform for sample size calculation, trial design, power analysis, and statistical planning — trusted by investigators worldwide.
Trusted by researchers at leading institutions
Clinical trial design is broken
Investigators waste weeks on sample size calculations using outdated tools and fragmented workflows.
Expensive Legacy Software
Enterprise tools like nQuery and PASS cost $1,000+ per year with clunky UIs from the 2000s.
Fragmented Free Tools
Dozens of disconnected web calculators with inconsistent formulas, no validation, and no audit trail.
No Guidance for Non-Statisticians
Investigators are forced to guess parameters without expert guidance on study design.
Everything you need to design a clinical trial
One platform. No spreadsheets. No guesswork.
Sample Size Calculators
12+ validated calculators for t-tests, proportions, survival, cluster RCTs, and more.
Trial Design Advisor
AI-powered recommendations for study design, endpoints, and parameter estimation.
Endpoint Library
Browse common endpoints by therapeutic area with published effect sizes and references.
Power & Sensitivity Analysis
Interactive power curves and sensitivity tables to explore your design space.
Document Suite
Export professional PDF reports, protocol sections, and statistical analysis plans.
Education Hub
Tutorials, guides, and worked examples for every calculator and design decision.
Try it now — no sign-up required
Two-Sample T-Test Sample Size Calculator
Study Parameters
Required Sample Size
126
63 per group × 2 groups
How it works
Describe your study
Tell us about your intervention, population, endpoints, and design preferences.
Get design recommendations
Our AI advisor suggests the optimal design and helps you estimate statistical parameters.
Calculate & export
Get validated sample sizes, power curves, and professional PDF reports for your protocol.
Loved by researchers
"ClinicalTrials.Tools saved us weeks of back-and-forth with our biostatistician. The power curves alone are worth the subscription."
Dr. Sarah Chen
Principal Investigator, University Medical Center
"Finally, a modern tool that handles non-inferiority calculations correctly. The sensitivity analysis is a game-changer for protocol development."
Dr. James Morrison
Biostatistician, Clinical Research Organization
"I use the free calculators for every grant application. The PDF reports are professional enough to include directly in my submissions."
Dr. Priya Patel
Associate Professor, School of Public Health
Simple, transparent pricing
Start free. Upgrade when you need more.
- 5 core calculators
- 20 calculations/month
- 3 PDF exports/month (watermarked)
- 1 saved project
- Community support
Save $98/year
- All 12+ calculators
- Unlimited calculations
- Unlimited clean PDF exports
- Unlimited projects
- AI Design Advisor
- Sensitivity analysis
- Priority support
Save $298/year
- Everything in Pro
- Up to 5 team members
- Shared project workspace
- Custom report branding
- Admin dashboard
- Dedicated support
- Everything in Team
- Unlimited seats
- SSO / SAML
- Audit logging
- Custom integrations
- Dedicated account manager
- On-premise option
Start designing better trials today
Free forever for basic calculations. No credit card required.