How much you will actually get

A one-kilogram batch does not fill a kilogram of product, and in skincare the losses are larger and less obvious than in most categories.

Where the batch goes

Four places. Vessel losses: emulsion clinging to the mixing vessel, the blender shaft and the transfer jug, which for a viscous cream is substantial. Filling losses in the funnel, nozzle or piston. Headspace, which is deliberate. And retained samples, which you should be taking from every batch.

The vessel loss is the big one and it scales badly downward: a small batch loses a much larger proportion to the same surfaces.

Evaporation is the invisible loss

The water phase is held hot, often for twenty minutes or more, and water evaporates. That does not only reduce yield, it changes the percentage composition of everything else in the batch.

A batch that lost three percent of its water has every other ingredient at a slightly higher concentration than the formula says, including the preservative and the actives.

Cover the vessel during heating, or weigh at the end of the hot stage and correct back with water before combining the phases. The second is more reliable and takes a minute.

Working out units per batch

Take the batch weight, subtract a realistic vessel and filling loss, subtract retained samples, then divide by the fill weight including your deliberate overfill.

Measure it once for each product and process rather than estimating, because the loss depends on viscosity and on your equipment and is stable enough to plan with afterwards.

Why the number matters more here

Because batch size is constrained by shelf life rather than capacity, so you cannot simply make extra. And because the per-formula testing cost is spread over the units a batch produces, which makes yield a direct input into whether a product is viable at all.

References