How Much Sunscreen Should You Actually Use?
Part of our guide: Building a Simple Skincare Routine Worth Rebuying
By the BasketLab team · updated 25 September 2026 · how we rank
Here's an uncomfortable truth: the SPF number on your bottle is a lab figure, achieved with a thick, even coat that almost nobody applies in real life. Skimp on the amount and your factor 50 quietly performs like a factor 15. So how much is enough? More than you're using. Let's be specific.
Most people apply less than half what the SPF rating assumes. Use roughly two teaspoons for the head, neck and arms, or about two tablespoons (6 to 8 teaspoons) to cover the whole body in swimwear. Reapply at least every two hours, and straight after swimming, towelling or heavy sweating.
The teaspoon rule, by body part
SPF numbers are measured in laboratories using 2mg of sunscreen per square centimetre of skin. Almost nobody applies that much in real life, which is why a well-applied SPF30 often protects better than a thin smear of SPF50.
| Area | Amount |
|---|---|
| Face, head and neck | Half to one teaspoon |
| Each arm | Half a teaspoon each |
| Each leg | One teaspoon each |
| Front of body | One teaspoon |
| Back of body | One teaspoon |
| Whole body total | About 6 to 8 teaspoons (2 tablespoons) |
For the face alone, the widely used shorthand is two fingers: a line of sunscreen along the length of your index and middle fingers.
How often to reapply
At least every two hours in the sun, and immediately after swimming, towel drying or heavy sweating, even if the bottle says water resistant. Water resistance means the SPF holds up for a period in water, not that it survives being rubbed with a towel.
The first application matters most: put it on 15 to 30 minutes before going out so it has time to form an even film, and do not forget ears, the back of the neck, the tops of feet and the hairline, which are the classic missed spots.
Does a higher SPF let you use less?
No, and this is the most common misunderstanding. SPF50 applied thinly can deliver less real protection than SPF30 applied properly, because the rating assumes that full 2mg per square centimetre. Higher SPF gives you a margin for error, not permission to skimp.
Also check for broad-spectrum or UVA protection (in the UK, a UVA logo or star rating), since SPF measures UVB only.
How long a bottle should last
This is a useful sanity check. If you are applying the right amount, a 200ml bottle provides roughly six to eight whole-body applications. A family bottle that lasts you all summer is a sign of under-application rather than good value.
Sunscreen also degrades: check the period-after-opening symbol, and replace anything left over from previous years rather than trusting it on a beach day.
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Common questions
How much sunscreen should I use?
About two teaspoons for the head, neck and arms, or roughly two tablespoons (6 to 8 teaspoons) to cover the whole body in swimwear. For the face alone, a line along your index and middle fingers is the common shorthand.
How often should you reapply sunscreen?
At least every two hours while in the sun, and straight after swimming, towel drying or heavy sweating, even with water-resistant products. Apply the first layer 15 to 30 minutes before going outside.
Is SPF50 twice as good as SPF30?
No. SPF30 blocks around 97% of UVB and SPF50 around 98%, so the difference is small. The bigger factor is how much you apply: a higher SPF gives a margin for error rather than allowing you to use less.
Does water-resistant sunscreen need reapplying?
Yes. Water resistance means the SPF holds for a stated period in water, typically 40 or 80 minutes, and towelling removes it regardless. Reapply after swimming or drying off.
How long should a bottle of sunscreen last?
Applied correctly, a 200ml bottle gives roughly six to eight whole-body applications. If a bottle lasts you a whole summer, you are almost certainly applying too little.