Sunscreen Application Calculator

Per Application (in ounces, teaspoons, or milliliters) is calculated purely from which body areas are toggled on -- face, neck, arms, legs, torso, back -- each contributing its own fixed fraction of a full-body ounce (lines 12-19, 29-31). Hours Outdoors and Reapply Every are never part of that formula; they only affect Total Applications and Total Needed, separate outputs computed afterward.

Total Applications is Hours Outdoors divided by the reapplication interval, rounded up to the next whole number with Math.ceil (line 34). At the default 4 hours outdoors, both a 2-hour and a 2.2-hour interval divide out to a value between 1 and 2, so both round up to the same 2 applications -- the output only changes once the division crosses a whole-number boundary, such as dropping the interval to 1.8 hours.

The calculator clamps the reapplication interval to a minimum of 0.5 hours with Math.max(reapplyInterval, 0.5) before dividing Hours Outdoors by it (line 33), which prevents the interval from ever reaching zero and producing an undefined or infinite Total Applications figure -- a safeguard that only matters if Reapply Every were set below the input's own 0.5-hour minimum.

Days per 6 oz Bottle divides a fixed 6-ounce bottle size by Total Needed for the day (line 39). If every body-area toggle is switched off, Total Needed comes out to exactly zero, and dividing by zero is avoided by returning 999 as a stand-in for "effectively never runs out" rather than an error or an infinite value.