Drops are are a really common way to measure small amounts of certain materials, especially for those creating soap or fragrances. A drop is however not a standard measurement unit which can be problematic when attempting to track your inventory correctly.
A Drop in itself is not an easy thing to quantify: its true size is defined by the dropper, the density and surface tension of the liquid and even the strength of its gravitational field.
It can however be recorded in an approximate way for inventory purposes and then refined once you learn more about your usage history. This method can be particularily useful if this is the only measurement unit that makes sense to manufacture in.
In general to begin with a good estimate of the size of a drop is 0.05 mL - this is effectively the standard used by pharmacists to determine the size of a drop so it's a good place to start.
You have two options from here to track your inventory using drops:
- Convert all your drop measurements into their equivalent approximate mL measurements (i.e. if you have a recipe calling for 5 drops, this would be recorded as 0.25mL)
- Convert your purchased bottles immediately into their drop equivalents (i.e. if you have a 250mL bottle, this would be approximately 5000 drops you have available)
The important thing to note with using drops is that you need to constantly keep in mind that your measurement is an approximate one. This means that you should be cycle counting any materials that are measured in drops on a regular basis to compare your stock levels to your recorded ones.
If you find that your physical stock count is significantly different to what your inventory software is telling you then you may wish to reassess the drop size: for example, if you find that you have much less on hand of an ingredient than you expected your drop size may actually be more accurately defined as a slightly larger amount (i.e. 0.06 mL) going forward. In the meantime, you'll want to record any adjustments to stock levels made until your stock counts are in sync.