The sunscreen amount calculator tells you exactly how much sunscreen to apply to get the SPF protection on the label. Studies show most people use only 25-50% of the recommended amount, cutting effective SPF in half. Select which body areas you're protecting to see the correct amount.
Select Areas to Protect
How to Apply the Right Amount of Sunscreen
The SPF number on your sunscreen bottle assumes you apply 2mg per square centimeter of skin — a standard derived from clinical testing. When you apply less, the effective protection drops significantly. SPF 50 with half the recommended amount becomes roughly SPF 12-15 in real-world protection.
The Teaspoon Rule
A useful shorthand: use about 1/4 teaspoon (1.25 ml) for the face and neck, and 1/2 teaspoon (2.5 ml) for each arm. Most full-body applications require about 1 full shot glass (approximately 35ml) of sunscreen to cover completely. This is much more than most people typically use.
Application Tips
Apply sunscreen 15-30 minutes before sun exposure to allow it to fully bind to skin. Dot it across the area rather than applying in one spot and rubbing — this ensures even distribution. Don't forget the back of the neck, ears, and tops of feet when outdoors in open shoes.
Frequently Asked Questions
Is this sunscreen calculator free?
Yes, completely free with no signup required.
How much sunscreen do I need for my face?
About 1/4 teaspoon (1.25 ml) for the face and neck combined. This is roughly a nickel-sized amount. Most people underapply significantly — using only 25-50% of the recommended amount, which reduces effective SPF dramatically.
What is the 2mg/cm² rule?
SPF ratings are tested at 2mg per square centimeter of skin surface. The teaspoon rule (1 teaspoon for full body) is an approximation of this. Applying less than the tested amount reduces actual SPF — SPF 50 becomes SPF 25 or less with half the application.
How long does a 3oz (100ml) sunscreen bottle last?
A 3oz bottle lasts approximately 10-15 full-body applications if applied correctly. For daily face-only use, the same bottle lasts 30-40 days. Most people get fewer applications than expected because they underapply.
How often should I reapply sunscreen?
Every 2 hours for outdoor activities. Immediately after swimming or heavy sweating. Reapplication is just as important as the initial application — no sunscreen provides all-day protection from a single application.