How much sunscreen do you actually need? For your face, neck and ears together, about one teaspoon. For your whole body in swimwear, about 35 ml, which is roughly seven teaspoons, or a little more than the shot glass the American Academy of Dermatology uses as its one-ounce reference. Pick the areas you’ll expose below and get your number.
Your sunscreen amount
Based on Cancer Council Australia’s guidance of at least one teaspoon per zone and the AAD’s one-ounce body reference. Bottle pumps vary too much between products to convert reliably, so measure with a real teaspoon once and learn what it looks like.
How this calculator works
The SPF number on any label is measured in a lab at a standardized layer of 2 mg of sunscreen per square centimeter of skin, and a dosage study by Taylor and Diffey in the BMJ showed that applying a realistic thinner layer delivers only about half the stated SPF [1]. Translating that lab thickness into kitchen units is what public health bodies have already done for you. Cancer Council Australia puts it at about 35 ml for an average adult’s full body, with at least one teaspoon each for your arms, legs, front, back, and face, neck and ears [2]. The American Academy of Dermatology’s version is about one ounce for the body, the amount that fills a shot glass, and about a teaspoon for the face [3]. The two land in the same ballpark, and this calculator simply adds up the teaspoon zones you select.
Two caveats. First, these are floor numbers for an average adult, so a larger frame needs more. Second, the amount only works if it stays on: reapply every two hours outdoors, and right after swimming or heavy sweating [2].
Packing for kids? The teaspoon-per-zone logic still applies, just with smaller zones, so scale each zone down rather than skipping any. Babies under 6 months are a special case: shade and clothing come first, per AAP guidance, and our kids and baby sunscreen guide covers those rules and the gentle picks in detail.
For the full story on why the amount matters more than the SPF number, read our guide to how much sunscreen to apply. Heading outside in shorts? The body sunscreen guide covers the products that make a full dose realistic.
Sources
[1] Taylor and Diffey, BMJ 2002 (labeled SPF is measured at 2 mg per square centimeter; realistic application delivers about half): link
[2] Advice on how to choose, apply and store sunscreen, Cancer Council Australia (about 35 ml or around 7 teaspoons full body; at least one teaspoon per zone; reapply every 2 hours and after swimming, sweating or towel-drying): link
[3] How to Apply Sunscreen, American Academy of Dermatology (about one ounce, a shot glass, for the body; about one teaspoon for the face): link
[4] Baby Sunburn Prevention, American Academy of Pediatrics via healthychildren.org (babies under 6 months: shade and clothing first; archived copy while the live page is down): link