Batch Formulas

How to Calculate Coating and Ink Batch Formulas: Yield, Letdown, and Viscosity

The core formulas every coatings and ink formulator runs daily, worked through with real weights, ratios, and units so you can reproduce them on the floor.

Batch math in coatings and inks starts with the formulation weight-up. A formula is stated in weight percent, and every component scales linearly to the batch size. For a 2,000 kg batch of a solventborne alkyd at 22% pigment, 35% resin solids, 8% additives, and 35% solvent, you multiply each percent by 2,000: 440 kg pigment, 700 kg resin, 160 kg additive, 700 kg solvent. Sum must equal batch weight to within 0.1%. Use the Pigment Usage, Resin Usage, and Solvent Usage calculators to convert percentages into a check-weighed batch card and confirm the components close to 100.0%.

Letdown ratio governs how a concentrated millbase gets extended into finished product. If you grind a 60% pigment dispersion and the finished paint needs 22% pigment, the letdown ratio is 22 divided by 60, or 0.367, meaning each 1.0 kg of millbase carries 0.367 kg of pigment. To hit 440 kg of pigment you need 440 divided by 0.60, which is 733 kg of millbase, then 1,267 kg of letdown vehicle to reach 2,000 kg. The Letdown Ratio calculator handles the inversion so you avoid the common error of dividing by finished percent instead of grind percent.

Batch yield compares good product packed out against theoretical batch weight. Theoretical is the summed weight-up; actual is what leaves the tank after filter losses, tank heel, and line purge. If a 2,000 kg batch nets 1,910 kg saleable, yield is 1,910 divided by 2,000, or 95.5%. The 90 kg gap breaks into roughly 25 kg tank heel, 40 kg filter and transfer holdup, and 25 kg fill-line purge. Run the Batch Yield calculator per batch so you can trend loss by source rather than accepting a single blended number that hides where material actually disappears.

Viscosity adjustment is a dilution calculation, not a guess. Blending viscosity does not average linearly, so use a log-blend approximation: log(final) equals the weight-fraction-weighted average of log(component viscosities). To drop a 1,200 cP base to 800 cP with a 50 cP thinner, solve for solvent fraction x in log(800) equals (1 minus x) times log(1200) plus x times log(50). That yields x near 0.13, so about 260 kg of thinner into a 2,000 kg batch. The Viscosity Adjustment calculator runs the log-blend and back-checks against your target Ford cup or Krebs reading.

Mixing time depends on tank geometry and the energy you need to disperse or dissolve. A useful basis is specific energy, in kilowatt-hours per metric ton. If a disperser draws 45 kW under load and the recipe needs 8 kWh per ton for full grind development, a 2.0 ton batch needs 16 kWh, so 16 divided by 45 is 0.36 hours, about 21 minutes at full draw. Add ramp and letdown passes. The Mixing Batch Time calculator converts installed power, target energy, and batch size into a cycle estimate you can slot into the schedule.

Fill throughput closes the loop from bulk tank to packed units. If a piston filler runs 24 heads at 18 fills per minute nominal but averages 82% of nameplate after changeovers and jams, effective rate is 24 times 18 times 0.82, or 354 units per minute. A 2,000 kg batch filled into 5.0 kg pails is 400 pails, so fill time is 400 divided by 354, about 1.13 minutes of pure run, plus setup. The Filling Line Throughput calculator separates nameplate from effective rate so your schedule reflects the 18% you actually lose.

Tie the chain together with a mass check across every stage. Weigh-up must equal batch weight, letdown must reconcile pigment carried in the millbase against target loading, and packed units times fill weight plus documented losses must equal the batch that entered the fill line. For the example, 400 pails times 5.0 kg is 2,000 kg gross, less 90 kg loss gives 1,910 kg, matching the 95.5% yield. When these three checks agree to within 1%, your batch card, letdown, and fill records are internally consistent and you can defend the numbers in an audit.

Published 2026-07-01.