SPF Formulation Calculator
UV filter percentages for target SPF from in-vitro data.
About this calculator
This calculator estimates sunscreen SPF from five UV-filter percentages using a simplified additive model, not in-vivo ISO 24444 testing. Each filter first earns a linear contribution: zinc oxide at 1.5 SPF points per percent, titanium dioxide at 2.0, avobenzone at 2.5, octinoxate at 3.0, and octocrylene at 1.0 (lines 32-38). Those contributions are summed with a baseline of 1 to produce a raw SPF figure (lines 41-45). When raw SPF exceeds 30, the engine applies a fixed linear 50% multiplier so only half of the excess above 30 counts toward Estimated SPF (lines 49-52). UVA-active percentage is zinc oxide plus avobenzone; UVB-active percentage adds titanium dioxide, octinoxate, octocrylene, and half the zinc oxide level (lines 56-57).
Broad Spectrum flags yes when the UVA-to-UVB ratio is at least 0.6 and UVA filters total at least 2% (lines 58-59). Photostability flags yes when octocrylene is at least half the avobenzone level or avobenzone is absent (line 68). UVB Protection Percent converts Estimated SPF through one minus one divided by SPF (line 71). Batch Size scales Total Filter Weight in grams only; it does not change Estimated SPF or the broad-spectrum and photostability flags (line 65).
Inputs
Results
Estimated SPF
28.5
UVB protection (%)
96.5
How to Use This Calculator
- Enter the concentrations of zinc oxide, titanium dioxide, avobenzone, octinoxate, and octocrylene in your sunscreen formula.
- Enter the batch size in grams to get the total filter weight needed.
- Review the estimated SPF, UVB protection percentage, and UVA/UVB filter totals.
- Check the broad-spectrum and photostability flags to see whether the filter mix qualifies as broad spectrum and whether octocrylene sufficiently stabilizes avobenzone.
- Adjust UV filter concentrations to reach the target SPF -- note this is a formulation estimate; in-vivo SPF testing per ISO 24444 is required for labeling.
How the result changes with Zinc Oxide (%)
| Zinc Oxide (%) | Estimated SPF | UVB protection (%) |
|---|---|---|
| 5 | 21 | 95.2 |
| 7.5 | 24.8 | 96 |
| 15 | 33 | 97 |
| 25 | 40.5 | 97.5 |
What each input means
- Zinc Oxide (%)
- Zinc oxide percentage. Broad-spectrum UVA+UVB. FDA max 25%. Contributes ~1.5 SPF per 1%.
- Titanium Dioxide (%)
- Titanium dioxide percentage. Mainly UVB. FDA max 25%. Contributes ~2.0 SPF per 1%.
- Avobenzone (%)
- Avobenzone (Parsol 1789) percentage. UVA filter. FDA max 3%. Contributes ~2.5 SPF per 1%.
- Octinoxate (%)
- Octinoxate (Octyl Methoxycinnamate) percentage. UVB filter. FDA max 7.5%. Contributes ~3.0 SPF per 1%.
- Octocrylene (%)
- Octocrylene percentage. UVB + photostabilizer for avobenzone. FDA max 10%. Contributes ~1.0 SPF per 1%.
- Batch size (g)
- Total batch weight for calculating filter weights.
What each result means
- Estimated SPF
- Estimated SPF based on UV filter concentrations. Note: actual SPF requires in-vivo testing.
- UVB protection (%)
- Percentage of UVB radiation blocked. SPF 15=93.3%, SPF 30=96.7%, SPF 50=98%.
- Broad spectrum? (1=yes)
- 1 if the formulation provides meaningful UVA protection (broad spectrum claim).
- Photostable? (1=yes)
- 1 if avobenzone is adequately stabilized by octocrylene or not present.
- Total UV filters (%)
- Combined percentage of all UV filters in the formulation.
- Total filter weight (g)
- Total grams of UV filters needed for the batch.
- UVA filters total (%)
- Combined percentage of UVA-active filters (zinc oxide + avobenzone).
- UVB filters total (%)
- Combined percentage of UVB-active filters.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersZinc Oxide (%) = 10, Titanium Dioxide (%) = 0, Avobenzone (%) = 3, Octinoxate (%) = 0 = 6 input(s) provided
- Calculate Estimated SPF28.5 = 28.5
- Calculate UVB protectionUVB protection = (1 - 1 / max(1, estimatedSpf)) * 10096.5 = 96.5
- Calculate Broad spectrum?1 = 1
- Calculate Photostable?1 = 1
Engine last updated . Checked against 3 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
Why does my Estimated SPF stop rising as quickly once filter levels get high?
The engine sums each filter's linear contribution into a raw SPF value, then applies dampening whenever that raw total exceeds 30: only half of the amount above 30 is added back on top of 30 (lines 49-52). This reflects diminishing returns at higher filter loadings that bench-scale linear models tend to overpredict compared with in-vivo panels.
What makes the Broad Spectrum flag turn on besides having UVA filters present?
Broad Spectrum requires two conditions together: UVA filter percentage must be at least 2%, and the ratio of UVA filters to UVB filters must reach 0.6 or higher (lines 58-59). UVA percentage is zinc oxide plus avobenzone; UVB percentage counts titanium dioxide, octinoxate, octocrylene, and half of the zinc oxide level (lines 56-57). A UVB-heavy mix can fail the ratio even with meaningful UVA actives on board.
Does Batch Size change Estimated SPF or only the filter weight output?
Batch Size affects Total Filter Weight in grams by multiplying batch weight by total filter percentage divided by one hundred (line 65). Estimated SPF, UVB Protection Percent, Broad Spectrum, and Photostability are computed entirely from filter percentages before batch weight enters the calculation, so doubling batch size doubles grams needed without moving the SPF estimate.
How does the calculator decide whether avobenzone is adequately stabilized?
Photostability reports yes when octocrylene concentration is at least half the avobenzone concentration, or when avobenzone is not present at all (line 68). If you include avobenzone without enough octocrylene co-filter, the flag stays off even though avobenzone still contributes to UVA totals and Estimated SPF through its own linear factor.
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