Sunscreen SPF Coverage
See how much UV an SPF blocks and how often to reapply.
About Sunscreen SPF Coverage
An SPF rating tells you how much UV is blocked: SPF 30 stops about 97 percent of UVB. No sunscreen fully blocks, so thumb-size amounts must be reapplied every couple of hours. Higher SPF is not a license to stay out longer, because protection fades with sweat and water, making reapplication timing just as important as the rating.
Formula
Sunscreen SPF Coverage
UV blocked = (1 - 1/SPF) x 100; reapply roughly every 2 hours
- SPF
- Sun protection factor rating of the product
Worked example
With the default values below, Sunscreen SPF Coverage returns UV Blocked of 96.67%. Change any input above and every figure here is recalculated in your browser.
Inputs used
- SPF ratingaccepts 1–100
- 30
- Daily exposure hoursminimum 0
- 2
- Skin typeone of Fair, Medium, Dark
- Fair
Results
- UV Blocked
- 96.67%
- UV Reaching Skin
- 3.33%
- Suggested SPF
- SPF 50+ recommended for prolonged exposure
Step by step
- 1Values used
- 2Sunscreen SPF Coverage
- 3UV Blocked= 96.67
- 4UV Reaching Skin= 3.33
- 5Suggested SPF= SPF 50+ recommended for prolonged exposure
Assumptions and limits
- The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Sunscreen SPF Coverage calculated?
UV blocked = (1 - 1/SPF) x 100; reapply roughly every 2 hours An SPF rating tells you how much UV is blocked: SPF 30 stops about 97 percent of UVB. No sunscreen fully blocks, so thumb-size amounts must be reapplied every couple of hours.
Why does Sunscreen SPF Coverage matter?
Higher SPF is not a license to stay out longer, because protection fades with sweat and water, making reapplication timing just as important as the rating.
What values do I need to enter?
This calculator takes 3 inputs: SPF rating, Daily exposure hours, Skin type. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.