Process tool
Tablet surface area and coating build-up calculator
Surface area per tablet and coating build-up in mg per square centimetre, which is how enteric coats are specified.
- Runs in the browserNothing is submitted anywhere
- Working shownCheck every line by hand
- Plant figuresThe bands our grades run in
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Written by the Rglax Pharma technical team, who formulate and manufacture every grade named on this calculator at our WHO-GMP works in Tahliwal, Una (drug manufacturing licence NNZ/23/238). Reviewed 3 September 2026. Licences and certificates.
Result
Surface area
4.335 cm²
Flat-faced approximation
- Coating applied
- 40 mg per tablet
- Build-up
- 9.23 mg/cm²
Inside the usual window of 4 to 12 mg/cm². Enteric coats usually target 6 to 10; below 4 gastro resistance is at risk and above 12 the film bridges the break line
- Assessment
- Typical enteric range
How this was worked out
- surface area = 2π(6)² + 2π(6)(5.5) = 4.335 cm²
- coating applied = 500 mg × 8% ÷ 100 = 40 mg
- build-up = 40 mg ÷ 4.335 cm² = 9.23 mg/cm²
Formula
surface area ≈ 2πr² + 2πrh build-up (mg/cm²) = coating applied (mg) ÷ surface area (cm²)
Why this number matters
Percentage weight gain hides a real problem. A small tablet has far more surface area per unit weight than a large one, so the same percentage gain gives a much thinner film on the small tablet. Enteric coating is specified in mg per square centimetre for exactly this reason, and gastro resistance failures on small tablets almost always trace back to someone scaling on percentage instead.
Where it goes wrong
This uses a flat-faced approximation. A deeply concave or capsule shaped tablet has more surface area than the formula gives, so treat the result as a floor rather than an exact figure.
Worked example
With tablet diameter of 12 mm, tablet thickness of 5.5 mm, core weight of 500 mg and weight gain of 8 %, the calculation gives:
- Surface areaFlat-faced approximation
- 4.335 cm²
- Coating applied
- 40 mg per tablet
- Build-up
- 9.23 mg/cm²
- Assessment
- Typical enteric range
The arithmetic is 2 lines, shown beside the result above so it can be checked by hand: surface area ≈ 2πr² + 2πrh; build-up (mg/cm²) = coating applied (mg) ÷ surface area (cm²).
Typical ranges
- Tablet diameter(mm)A 500 mg round tablet is usually 11 to 13 mm
These are the bands our grades were developed in at Tahliwal. A run outside them is not wrong, but it is a run the published parameters no longer describe.
Other calculators
- Coating weight gainHow much dry coating material a batch needs at a target percentage weight gain, including process loss.
- Coating dispersionWater or solvent needed to disperse a ready-mix powder at a given solids concentration.
- Spray rateSpray rate per gun and total run time from your dispersion quantity and available process window.
- Pan speedTangential bed velocity from pan diameter and RPM, with the range most film coating runs sit in.
- Drying capacityHow much water your inlet air can actually carry away, and the spray rate that supports.
- Dispersion vesselVessel volume, diameter and impeller size for the dispersion quantity you are making.
Every grade page carries the process parameters it was developed on, so you can start from a known point rather than a calculated one. Browse the grades.
Read next
- Film coating systemArea is what the coat has to cover, so it sets the quantity every other figure is derived from.
- The grades and their parametersEach grade page states the build-up it was developed at.
- Tablet coating weight gain calculatorHow much dry coating material a batch needs at a target percentage weight gain, including process loss.
- Coating dispersion and solids calculatorWater or solvent needed to disperse a ready-mix powder at a given solids concentration.
- Coating spray rate calculatorSpray rate per gun and total run time from your dispersion quantity and available process window.
- Coating defects, and what causes themWhat the bed looks like when this number is wrong, and which parameter to move.
Need a second opinion
Talk to our technical team.
Send the core, the coater and the target and we will tell you what we would run, and which grade we would run it with.
From the calculation to the pan.