The common differences among Blend Uniformity, Weight Variation and Content Uniformity are mentioned below - 

  • Blend uniformity is an in-process test that is useful for ensuring the adequacy of the mixing of active pharmaceutical ingredients (APIs).
  • Content uniformity ensures that each dosage form includes the equivalent amount of active pharmaceutical ingredient or drug substance.
  • Weigh variation test of pharmaceutical product is an in-process test to ensure the weight of the finished product is within range.


  • The number of locations sampled in the blend should be sufficient to adequately “map” it, and target problematic areas such as above discharge valves and along the center axis of rotation.
  • For content uniformity sample should be collect form at least 30 locations spaced equally across the batch, including the beginning and end of the run.
  • For weight variation measurement weigh 20 tablets individually, and calculate the average weight. The requirements are met if the weights of NMT 2 of the tablets differ from the average weight by more than the percentage listed in pharmacopoeia. 


  • Failure of blend uniformity doesn’t lead to batch rejection.
  • Failure of content uniformity lead to batch rejection.
  • Failure of weight variation may lead the batch failure to meet the Assay limit.


Difference between Uniformity of dosage units and Uniformity of content

As per USP General Chapter 905, the uniformity of dosage units can be demonstrated by either of two methods, Content Uniformity or Weigh Variation.

  • Content uniformity test is applicable for hard capsules, uncoated tablets, or film-coated tablets containing less than 25 mg of drug substance comprising less than 25%, by weight, of the dosage unit.
  • Uniformity of dosage unit by weight variation test is applicable for hard capsules, uncoated tablets, or film-coated tablets containing 25 mg or more of a drug substance comprising 25% or more by weight of the dosage unit.

Weight variation test calculation formula

Weight variation tolerance:



Difference between content uniformity and assay

The major difference is content uniformity is measured for individual sample, where assay is measured for multiple sample simultaneously.


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