Skip to main content
Calcimator

SPF Effective Protection Calculator

Calculate your actual UV protection based on SPF rating, application thickness, and time since application.

Inputs

%
min

Results

Current Effective SPF

1.7

Current UVB Blocked41%
Label UVB Blocked (full application)96.7%
Reapply In20 min
Label SPF30
How to Use This Calculator
  1. Enter the SPF rating printed on your sunscreen label.
  2. Set the application amount as a percentage of the recommended 2 mg per cm2 (most people apply about 50%).
  3. Enter the number of minutes since you last applied sunscreen.
  4. Toggle the Swimming/Sweating option if you have been in water or exercising.
  5. Input the current UV Index from your weather app.
  6. Review Current Effective SPF and Reapply In time to know exactly when to reapply.

How the result changes with Application Amount

Application AmountCurrent Effective SPF
19%1
42%1.3
69%3.6
91%10.8

What each input means

SPF Rating
SPF number on the sunscreen label
Application Amount
Percentage of recommended amount applied (most people use ~50%)
Minutes Since Applied
Time since last sunscreen application
Swimming / Sweating
Water exposure accelerates degradation
UV Index
Current UV index (check weather app)

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    SPF Rating = 30, Application Amount = 50, Minutes Since Applied = 60, Swimming / Sweating = 0 = 5 input(s) provided
  2. Calculate Current Effective SPF
    1.7 = 1.7
  3. Calculate Current UVB Blocked
    Current UVB Blocked
    41 = 41
  4. Calculate Label UVB Blocked
    Label UVB Blocked
    96.7 = 96.7

Engine last updated . Checked against 2 independently-derived tests — how we verify calculators.

Related Calculators

The questions that sit next to this one — chosen by subject, including calculators filed under a different category.

Skincare

Sunscreen Application Calculator

Calculate how much sunscreen you need for full coverage based on body areas and time outdoors.

Skincare

Skin Hydration Calculator

Calculate your daily water intake and humectant needs for optimal skin hydration based on skin type and climate.

Dermatology

Sun Protection Calculator

Calculate safe sun exposure time, reapplication schedule, and sunscreen needs based on UV index, skin type, and SPF.

Cosmetics Formulation

SPF Formulation Calculator

UV filter percentages for target SPF from in-vitro data.

Weather & Climate

UV Index Calculator

Assess UV exposure risk based on UV index, skin type, altitude, and snow cover. Get personalized burn time and SPF recommendations.

More in Beauty, Fashion & Personal Care.