MaineblockFree download
Sample-size worksheet
The two-proportion sample-size calculator as an Excel workbook — same math as the online tool, but yours to keep, share, and drop into study protocols.
What's inside
One clean sheet: yellow input cells for baseline rate, target rate, α, power, and expected dropout; every result computed with live Excel formulas (NORM.S.INV under the hood — no macros, no plugins). Change an input and the required n updates instantly. Includes a notes block explaining the normal approximation and when it breaks down.
Free for any use, including commercial work. No email required.