Tablet Diameter Test

Tablets are compressed in the pharmaceutical industries using different types of toolings including punches & dies on compression machines.

Tooling shape and dimensions play an important role to compress the same size & shaped tablets during compression of each batch to maintain batch to batch consistency in terms of shape & diameter/dimensions.

Tablet Diameter

Tablet diameter is dependent on the dimensions of the punch tip or punch face so it is critically checked or verified before installation of tooling on the compression machine.


The tablet diameter or dimensions are mentioned on the first page of the Batch Manufacturing Record (BMR) to ensure that the same-size tablets are compressed all the time during compression of a specific batch using specified tooling.


Suppose we want to compress a batch of tablets in a round shape having a diameter of 9.0 mm.

So for this purpose, we will use round-shaped punches & dies. To produce 9.0 mm round tablets the diameter of punches used should always be 9.0 mm.

If we want to compress oblong-shaped tablets having a dimensions/diameter of 20×10 mm we will use oblong tooling having dimensions of 20×10 mm.

Common Question

A common question comes to mind

How can we check or verify the diameter of tablets before compression because we have not compressed any tablets yet?

The simple answer is by verifying the tooling diameter/dimension e.g the dimensions of the punches.

Tooling Verification

The tablet diameter testing is an unofficial test so most of the person in the pharmaceutical industry do not give much importance to it, but it is most critical check because if our tablet diameter or dimensions are not according to specifications it will create problems not only during tablet blistering but will also lead to deviation and batch reprocessing.

So the best practice is that during the compression machine setup, the tooling dimensions must be verified by the compression machine supervisor and Compression section pharmacist.

How To Check Punch Tip Dimensions?

The punch tip dimensions are measured using vernier calipers and if it is according to the BMR then install the tooling on the compression machine to start the compression process.

The reason behind this practice is that if the tooling dimensions will be according to BMR it will automatically produce the required size tablets.

Wrong Practice

In the Pharmaceutical industry, it is common practice that supervisors or pharmacists do not check or verify whole punch sets, instead, they only measure the dimensions of only one or two punches.

It is the wrong practice and it may result in critical impacts because there may be one punch in the whole punch set having the same shape but a slightly different dimension which may be wrongly placed during tooling storage.

So always verify a complete set of punches to avoid any process damage.

Procedure For Measuring Tablet Diameter

Like the tablet thickness test, the diameter of tablets is also measured using vernier calipers.

After line clearance we compress some tablets for Inprocess testing and during in-process testing Tablet diameter is checked or verified by the QA officer using the vernier Caliper.

Before delivering samples to the QA department the production pharmacist checks the tablet diameter in the compression machine room using a vernier caliper.

If tablets are round simply, we measure the diameter by placing round tablets in the jaws of the vernier caliper one by one and take readings displayed on the digital vernier caliper.

In the case of an oblong tablet, we measure dimensions according to BMR.  


If it is 20×10 mm mentioned in BMR it means the tablet length should be 20 mm & tablet width should be 10 mm.

So first we measure the length of the tablet using a vernier caliper & then the width of the tablet & it should be according to the BMR.

Relation Between Tablet Diameter / Dimension & Tablet Blistering

As we discussed earlier a specific product batch is compressed using specific tooling in the same way tablets are blistered on a blister machine using specific blister die plates nearly having the same pocket size as for compression tooling.

So If we compress tablets using the wrong dimension tooling it will not be possible to blister the tablets using its specified blister tooling plates.

Also Read

Tablet Hardness Test 

Thickness Test For Tablets

Function Of Blank Dies In Compression Machine

Stages and Mechanism of Tablet Compression.

Advancements in tablet compression machines.

Calculation of compression machine capacity.