Sunscreen Calculator

By: Patrick Myers Patrick Myers is the CEO and Founder of Calculator Academy. He has over eight years of experience developing online calculators and holds a B.S. in Mechanical Engineering. His work focuses on formula implementation, calculator accuracy, unit conversions, and creating practical tools that are easy to use.

Last Updated: August 3, 2026

Estimate sunscreen per application, reapplication timing, and bottles to pack from exposed skin, time outdoors, group size, and bottle size.

Quantity uses 2 mg/cm² and BSA scaling; grams and milliliters are treated as approximately equal.

Sunscreen Quantity Formula

This calculator estimates how much sunscreen to apply to exposed skin. It uses the Mosteller body-surface-area equation, a selected exposed-area fraction, and the 2 mg/cm² application amount used in standardized SPF testing.

BSA (m²) = √((heightcm × weightkg) ÷ 3600)
Exposed area (cm²) = BSA × 10,000 × coverage fraction
Sunscreen (g) = exposed area × 2 mg/cm² ÷ 1,000

For planning, the calculator treats one gram as approximately one milliliter. Product density varies, so the package directions and labeled volume remain the controlling instructions.

Application and Trip Planning

In application mode, the result is the estimated grams, milliliters, teaspoons, and US fluid ounces for one application. In trip mode, the calculator estimates applications per person per day, total milliliters, and whole bottles to pack.

Applications per day = max(1, round up(outdoor minutes ÷ selected planning interval))
Total mL = mL per application × applications × people × days
Bottles = round up(total mL ÷ bottle size)

The coverage presets are planning fractions, not anatomical measurements. Choose a custom percentage when the preset does not match the skin that will actually be exposed.

How to Use the Estimate

  • Apply sunscreen generously before exposure and follow the product label.
  • FDA guidance says to reapply at least every two hours and more often after swimming or sweating; water-resistant labels state whether the product remains effective for 40 or 80 minutes while swimming or sweating; those durations do not replace the general direction to reapply at least every two hours and after towel drying.
  • Use broad-spectrum sunscreen and combine it with shade, protective clothing, and other sun-protection measures.
  • This calculator estimates quantity only. It does not predict a safe exposure time or diagnose sun damage.

Example

For a person who is 170 cm tall and weighs 70 kg, the Mosteller BSA is about 1.82 m². With full-body coverage, the 2 mg/cm² model estimates about 36.4 g, or approximately 36.4 mL, per application. Clothing and the actual exposed-area selection can substantially reduce that amount.

Sources

  • U.S. Food and Drug Administration, Sunscreen: How to Help Protect Your Skin from the Sun.
  • U.S. Food and Drug Administration, Labeling and Effectiveness Testing: Sunscreen Drug Products for Over-the-Counter Human Use.