CH 19 · notes
How it works
USP <905> Uniformity of Dosage Units (harmonized; official 1 August 2023) judges content uniformity with an acceptance value. Assay each unit and express the result as a percentage of label claim. The acceptance value is AV = |M − mean| + k × s, where s is the sample standard deviation (n−1). The acceptability constant k is 2.4 for the first 10 units and 2.0 for 30 units. The chapter does not define k for any other count.
The reference value M depends on the target content T. Unless the monograph says otherwise, T is 100.0% of label claim, which is case 1 (T ≤ 101.5). Then M is the mean when the mean is from 98.5 to 101.5, 98.5 when the mean is lower, and 101.5 when the mean is higher. Case 2 applies only when T is above 101.5: the upper edge of M becomes T instead of 101.5. A manufacturing overage that merely offsets process loss is not a reason to set T above 100.
L1, 15.0 unless the monograph says otherwise, is the maximum acceptance value at both 10 and 30 units. If the 10-unit AV is above L1, the chapter says to test 20 more units. L2, 25.0 unless otherwise specified, is not an AV limit of 25. It is used only on the 30-unit set: no individual result may be below [1 − 0.01×L2]×M or above [1 + 0.01×L2]×M. With L2 = 25 that range is 0.75M to 1.25M. Mean, SD, and AV on this page are half-up to 2 decimal places, the same reporting as the USP <905> FAQ check table, and the L1 comparison uses that reported AV. The sample standard deviation is the same n−1 form as the RSD calculator.
This page does not decide content uniformity versus weight variation, and it does not estimate content from unit weights. Enter results that are already percent of label claim, or assay amounts with the label claim. Last checked 2026-10-31.
Not a substitute for compendial judgment. This applies the USP <905> content uniformity acceptance value only. Confirm the monograph, target T, and the current pharmacopeia text.
Worked example
USP <905> FAQ data set 1, ten results in percent of label claim, T = 100, L1 = 15.0. Load example fills the same numbers. Mean 100.40, SD 5.82, M = mean, AV 13.97, which meets the 10-unit criterion.
Sources
- USP <905> Uniformity of Dosage Units — PDG sign-off, official 1 Aug 2023; AV = |M − mean| + ks; harmonized with Ph. Eur. 2.9.40 and JP
- USP <905> Uniformity of Dosage Units FAQs — L1 limits AV at both stages; L2 is the 30-unit individual range; three check data sets
FAQ
What is the USP <905> acceptance value?
The acceptance value is AV = |M − mean| + k × s. The mean and each result are percent of label claim. s is the sample standard deviation (n−1). k is 2.4 for 10 units and 2.0 for 30 units. M is a reference value that equals the mean when the mean sits in the chapter’s interval, and an edge of that interval otherwise.
What is the difference between L1 and L2?
L1 (15.0 unless the monograph says otherwise) is the maximum acceptance value at both 10 units and 30 units. L2 (25.0 unless otherwise specified) is not an acceptance-value limit of 25. It is used only after 30 units have been tested, to decide whether any individual result is outside [1 − 0.01×L2]×M to [1 + 0.01×L2]×M.
When does case 2 apply?
Case 1 applies when the target content T is 101.5% of label claim or less. Unless the monograph says otherwise, T is 100.0%, so case 1 is the usual path. Case 2 applies only when T is above 101.5, and then the upper reference value is T instead of 101.5. A process overage that is meant to finish near 100% of label claim does not by itself set T above 100.
Does an AV above L1 on 10 units fail the batch?
Not by itself. USP <905> says to test 20 additional units and judge all 30. The 30-unit set must have AV at or below L1, and no individual result outside the L2 range of M.
Does this replace compendial judgment?
No. Not a substitute for compendial judgment. This applies the USP <905> content uniformity acceptance value only. Confirm the monograph, target T, and the current pharmacopeia text. Values were last checked 2026-10-31.