SPF Reapplication
Plan sunscreen reapplication for a full outdoor day.
About SPF Reapplication
The outdoor day is divided by the reapply interval to count touch-ups, plus the initial application. Sunscreen fades with sweat and exposure, and missed reapplication is the biggest cause of burns.
Formula
SPF Reapplication
Reapplications = ceil(hours / reapply window) - 1
- reapply window
- Approx. time lab data says sunscreen stays effective
Worked example
With the default values below, SPF Reapplication returns Reapplications of 1. Change any input above and every figure here is recalculated in your browser.
Inputs used
- SPFone of SPF 30, SPF 50, SPF 100
- SPF 30
- Outdoor hoursminimum 0.5 h
- 4 h
- Reapply everyminimum 0.5 h
- 2 h
- Per applicationminimum 0.5 ml
- 8 ml
Results
- Reapplications
- 1
- Initial Protection
- 120 min
- Total Sunscreen
- 16.0 ml
Step by step
- 1Values used
- 2SPF Reapplication
- 3Reapplications= 1
- 4Initial Protection= 120 min
- 5Total Sunscreen= 16.0 ml
Assumptions and limits
- The result is derived only from the 4 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 1 decimal place, 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 SPF Reapplication calculated?
Reapplications = ceil(hours / reapply window) - 1 The outdoor day is divided by the reapply interval to count touch-ups, plus the initial application.
Why does SPF Reapplication matter?
Sunscreen fades with sweat and exposure, and missed reapplication is the biggest cause of burns.
What values do I need to enter?
This calculator takes 4 inputs: SPF, Outdoor hours, Reapply every, Per application. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.