How the Coating Material Calculator works

Film coating adds a thin layer to the outside of a tablet, and the amount of material needed depends on the weight gain you are targeting relative to the uncoated core. The calculator starts from the core tablet weight, the target weight gain and the batch quantity, and works out how much dry coating material the batch needs.

Coating is applied as a dispersion or solution, not as a dry powder. The calculator therefore converts the dry requirement into a total suspension weight using the solid content of your coating dispersion. What remains after the solids are removed is the water or solvent to prepare. If a spray rate is entered, it also estimates how long the spraying phase should take.

Video walkthrough

Coating quantities

Example: 3% gain on a 400 mg core

Core tablet weight 400 mg, target weight gain 3%, batch 500,000 tablets, coating dispersion with 15% solids, spray rate 300 g/min.

1. Coating gain per tablet = 400 × 0.03 = 12 mg
2. Total dry coating = 12 mg × 500,000 = 6,000,000 mg = 6.0 kg
3. Total suspension weight = 6.0 ÷ 0.15 = 40.0 kg
4. Vehicle = 40.0 − 6.0 = 34.0 kg
5. Estimated spray time = 40,000 g ÷ 300 g/min = 133.3 min

The suspension is prepared with an allowance for line priming, overspray and pan losses, as defined in your batch record, so the quantity actually made is higher than 40.0 kg.

Weight gain targets and checks

• Weight gain: use the target and range in the approved process. Many aqueous film coats target about 2–4% of the core weight, but the validated range for your product is the one that counts.
• Solid content: the percentage must include every solid in the dispersion, such as polymer, pigment, plasticizer and opacifier, not the polymer alone.
• Weight gain check: confirm it by weighing a defined number of tablets before and after coating, and compare with the target. See Coating Weight Gain Troubleshooting.
• Reconciliation: the coating material used must be reconciled against the dispensed quantity. See Coating Reconciliation.

Typical errors in coating quantities

• Calculating gain on the coated tablet weight instead of the core weight.
• Mixing up weight gain percentage with solid content percentage.
• Counting only the polymer as solids and leaving out pigment and plasticizer.
• Preparing exactly the calculated suspension with no allowance for losses, so it runs out mid-batch.
• Using a spray rate from a different pan size or product when estimating process time.

Using the result at the dispensing and preparation stage

The dry coating quantity is the figure to dispense, and the suspension weight is the figure to prepare. Keep both in the batch record, together with the solid content used in the calculation, since a change in the solid content of the dispersion changes the quantity of liquid needed for the same dry weight. Record the actual quantity prepared and the quantity left in the lines and the vessel at the end of spraying, so the coating material can be reconciled afterwards.

Standards and references

The checks on this page relate to the documents below. Standards are revised from time to time, so confirm the current edition and follow your own approved procedures.

• 21 CFR 211.186, Master production and control records
• 21 CFR 211.101, Charge-in of components
• 21 CFR 211.103, Calculation of yield

Questions on coating material

How much weight gain is typical for film coating?

Aqueous film coats commonly target roughly 2–4% of the core weight. Modified-release and enteric coats usually need more, so follow your product’s validated figure.

Why convert dry coating into a suspension weight?

Because the coating is sprayed as a liquid. The suspension weight tells you how much dispersion to prepare, and the solids and vehicle quantities tell you what to dispense.

Does the calculator include spray losses?

No. It gives the theoretical requirement. Add the loss allowance your process has shown during validation.

Can I use it for capsules?

Yes, if the capsule is coated, enter the capsule weight as the core weight.

Related tools and guides: Coating Pan Loading · Tablet Coating Defects · Tablet Weight Calculator · Coating Reconciliation · Coating Weight Gain Troubleshooting

By Sajjad Ahmad. For reference and education only; verify limits against your SOPs and the current pharmacopoeia. See the methodology.