What Reproducibility actually tests, what mg/dosage and % Recovery mean, how System Suitability and %RSD fit in, and how the Combine %RSD of Precision is meant to work — including a common spreadsheet mistake that quietly breaks it.
Precision under ICH Q2(R2) measures how close a series of results are to each other under specified conditions — it has three levels: repeatability (same analyst, same day, same equipment), intermediate precision (different day/analyst/equipment within one lab), and reproducibility (between different laboratories, typically only assessed in collaborative/method-transfer studies).
The two are easy to mix up because they're tested the same way — a second run compared back against your original Repeatability data — but the lab tells them apart: Intermediate Precision is when testing is performed in the same laboratory, on a different instrument. Reproducibility is when testing is performed in a different laboratory. This calculator lets you pick whichever one correctly describes where your second dataset was generated (see Section 3 below) — the math never changes, only the label.
Each sample row uses its own Weight of Sample in the calculation — not one weight reused for every row. Locking every row to a single weight cell is a common spreadsheet mistake that quietly understates the true %RSD. The API Factor is optional: leave it blank and the standard formula applies exactly as above; enter a value and it multiplies straight into the Dilution Factor, everywhere — the results table, the math log, and the printed report all switch to the "with API Factor" version automatically.
The calculator opens with a Step 0 — Choose Mode toggle: Precision Reproducibility or Intermediate Precision. Both use the exact same formulas and calculation logic — every label on the page (the title, section headers, result cards, chart legend, math log, and the "Test:" field on the printed report) simply updates to match your choice. What differs is the testing condition the data actually represents: Intermediate Precision applies when testing is performed in the same laboratory, on a different instrument (see Section 1). Reproducibility applies when testing is performed in a different laboratory. Pick whichever one matches how your data was actually generated, not just whichever your SOP happens to call it by habit.
Two more selectors sit above the data-entry tables:
The Combine %RSD is meant to show the overall spread once you pool your Repeatability results (day 1) and Reproducibility results (day 2 / analyst 2) into one dataset, then take that dataset's %RSD:
A subtle spreadsheet bug to watch for: if the STDEV range and the AVERAGE range don't cover the exact same combined cells, you can end up dividing the standard deviation of one dataset by the average of a different dataset. The number still looks plausible — it just no longer answers "how much does the whole method vary?" This calculator combines both datasets into a single array before computing STDEV and AVERAGE, so numerator and denominator always match.
Exact limits always come from your own validation protocol/SOP, but these are commonly seen in industry:
| Metric | Typical Limit |
|---|---|
| System Suitability %RSD | ≤ 2.0% (standard replicate injections) |
| Reproducibility / Intermediate Precision %RSD | ≤ 2.0% (common assay spec) |
| Combine %RSD of Precision | ≤ 2.0% (combined Repeatability + Reproducibility) |