How to Calculate SPF?

Calculating the SPF value of a sunscreen formula is not a simple mathematical calculation based on the percentage of each sunscreen ingredient. The SPF value indicated on a sunscreen product is determined through standardized testing, either in vitro (in a lab) or in vivo (on human subjects).

The effectiveness of sunscreen ingredients in a formula depends on several factors, including:

• The concentration of each sunscreen agent.
• The synergistic effects between different sunscreen agents.
• The type of formulation (e.g., cream, lotion, spray).
• How well the product spreads and forms a uniform film on the skin.

Therefore, even if you know the ingredients and their percentages, you cannot accurately calculate the final SPF value directly from the formula. Testing is required to determine the actual SPF.

You mentioned using Zinc Oxide, Titanium Dioxide, and OMC (Octyl Methoxycinnamate) in your formula. Zinc Oxide and Titanium Dioxide are physical sunscreen agents that work by reflecting or scattering UV radiation. OMC is a chemical sunscreen agent that absorbs UV radiation.

While I could find information on various types of Zinc Oxide and Titanium Dioxide suitable for sunscreen formulations, I was unable to find information specifically on OMC using the available tools.

Some examples of Zinc Oxide and Titanium Dioxide products suitable for sunscreen formulations include:

• Zinc Oxide Transparent Dispersion (C12-15 alkyl benzoate Base)
• Zinc Oxide 40nm Dispersion (Water Base)
• Zinc Oxide Transparent Dispersion (Isopropyl Palmitate Base)
• Titanium Dioxide Transparent (15nm, Water-Dispersion)
• Titanium Dioxide 30nm SilkTouch™ (Polymethylsilsesquioxane Treated)

Remember, to know the true SPF of your formula, you would need to send it for laboratory testing according to relevant standards.