Roughly a teaspoon for the face and neck, and about six to eight teaspoons for a whole body. Most people apply less than half of that, which means they get less than half the stated protection.
- Face and neck: about a teaspoon, or two fingers' length squeezed onto the index and middle finger.
- Whole body: six to eight teaspoons, around 35ml, which is more than most people expect.
- Apply before you go out, not after, and reapply every two hours outdoors.
- Reapply after swimming or towelling, whatever the bottle claims about water resistance.
- Do not forget ears, the back of the neck, the tops of feet and the hairline.
SPF is measured at 2mg per square centimetre, which is far more product than people apply. Half the amount does not give half the SPF, it gives considerably less, so an SPF50 applied thinly can behave like an SPF15.
The protection factor is a laboratory measurement at a defined thickness. The gap between that thickness and real-world application is the single biggest reason sunscreen underperforms.
This is general information, not medical advice, and it does not replace a GP, a pharmacist or NHS 111. Call 999 in an emergency. Full disclaimer.