Sunscreen calculator
Almost everyone under-applies SPF — and under-applying cuts your protection sharply. Pick what you're covering and how long you're out, and we'll tell you exactly how much to use.
Your day in the sun
Two-finger rule: for your face and neck, a line of sunscreen along your index and middle fingers is about the right amount.
How this works
SPF is lab-tested at 2 mg of product per square centimetre of skin. Translated into real life, that's the widely used teaspoon rule:
- Face, neck & ears — about 3 ml (½ teaspoon)
- Each arm & hand — about 3 ml (½ teaspoon)
- Each leg & foot — about 6 ml (1 teaspoon)
- Chest & stomach — about 6 ml (1 teaspoon)
- Back & shoulders — about 6 ml (1 teaspoon)
That adds up to roughly 33 ml for a full body — about a shot glass. We apply once up front, then once more every two hours you're outside. Reapply straight away after swimming, towelling off, or heavy sweating, no matter what the clock says.
Frequently asked questions
How much sunscreen should I actually use?
A full adult body needs about 33 ml — roughly 7 teaspoons, or a shot glass. Broken down that is about half a teaspoon (3 ml) for your face, neck and ears, a teaspoon for each arm, two teaspoons for each leg, and a teaspoon each for your chest and back.
How much sunscreen do I need for my face?
About 3 ml, which is roughly half a teaspoon. A popular shortcut is the two-finger rule: squeeze sunscreen along the length of your index and middle fingers, then apply that to your face and neck.
How often should I reapply sunscreen?
Every two hours while you are in the sun, and straight after swimming, towelling off or heavy sweating. This calculator assumes one application up front plus a reapplication every two hours.
Does using less sunscreen lower the SPF?
Yes. SPF is tested at 2 mg per square centimetre of skin. Applying half the amount gives you far less than half the labelled protection, which is why measuring matters more than chasing a higher SPF number.
Educational only, not medical advice. Sunscreen is one part of sun safety — shade, clothing and timing matter too. Read our disclaimer.