Calculator
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.
Result
- Surface area
- 4.335 cm²Flat-faced approximation
- Coating applied
- 40 mg per tablet
- Build-up
- 9.23 mg/cm²
- Assessment
- Typical enteric rangeEnteric coats usually need 6 to 10 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.
Other calculators
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.