Calculating Powder Percentage in Shampoo Formulation Measured by Volume
Question
I am making shampoo and can measure the final product in ml. I ordered an ingredient from MySkinRecipes which is a powder measured in grams. The formula states to add `0.2%`. How do I add this? How do I convert the percentage by weight to volume?
Answer
Okay, I understand you're trying to figure out how to add a powder ingredient specified as 0.2% by weight into a shampoo formulation that you measure in milliliters.
Converting a percentage by weight (% w/w) of a powder ingredient into a volume (ml) to add to a liquid formulation measured in volume (ml) can be tricky because you need to account for density.
Here's the general approach and explanation:
- Percentage in formulations is usually by weight: When a formula specifies a percentage for a powder ingredient, it almost always means percentage by weight of the total formulation weight (% w/w).
- You need the total weight of your shampoo: To calculate 0.2% by weight, you first need to know the total weight of the shampoo you are making, not just the volume.
- Convert shampoo volume to weight: To get the total weight from the total volume (ml) of your shampoo, you need the density of the shampoo. Most shampoos have a density close to water (around 1 g/ml), but it can vary depending on the ingredients.
- Total Shampoo Weight (g) = Total Shampoo Volume (ml) * Density of Shampoo (g/ml)
- Calculate the weight of the powder needed: Once you have the total weight of the shampoo formulation, you can calculate the weight of the powder ingredient needed.
- Powder Ingredient Weight (g) = (0.2 / 100) * Total Shampoo Weight (g)
Example:
Let's say you are making 100 ml of shampoo, and you estimate the density of your shampoo is about 1.05 g/ml.
- Total Shampoo Weight = 100 ml * 1.05 g/ml = 105 g
- Powder Ingredient Weight = (0.2 / 100) * 105 g = 0.002 * 105 g = 0.21 g
So, you would weigh out 0.21 grams of your powder ingredient and add it to your 100 ml (which weighs 105 g) of shampoo base.
Why not convert the powder to ml?
Converting the powder's weight to a volume (ml) directly is usually not practical or accurate for small amounts in a formulation. You would need the bulk density of the powder, which can vary, and measuring very small volumes of powder is difficult. It's much more accurate to weigh the powder.
In summary:
Calculate the amount of powder needed based on the total weight of your shampoo formulation. You'll need to know or estimate the density of your shampoo to convert its volume to weight.
I hope this helps clarify how to approach this!