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Sunscreen Calculator

Created by Julia Żuławińska and Aleksandra Zając, MD
Reviewed by Jack Bowater
Last updated: Jan 18, 2024


Who of us wouldn't like to lie down on some exotic beach with a cool drink in hand, not having to worry about anything except what to have for dinner? 🏖️ Or maybe you're a sporty type and would prefer to spend your time more actively, for example, visiting Greek ruins or hiking through the Grand Canyon? Whether you want to look white as a cautious dermatologist or as bronzed as a Baywatch lifeguard, with this calculator, you will find out how much sunscreen you should apply to keep your skin safe and how many packets you need to take with you on vacation. ☀️☀️

Prefer watching over reading? Learn all you need in 90 seconds with this video we made for you:

Why do we need sunscreen?

Every day we are exposed to different types of radiation: infrared, visible light, and some ultraviolet (UV). The latter is short wavelength radiation (100-400 nm) and therefore potentially harmful to our health. We divide it into three categories:

  • UVA (320 - 400 nm), which penetrates the skin;
  • UVB (280 - 320 nm), blocked by the epidermal layer of our skin; and
  • UVC (wavelengths of 100 - 280 nm), blocked by the ozone layer in the atmosphere.

The intensity of UVB radiation depends on the time of day, weather, and latitude (it's stronger at the equator). UVA not only penetrates deeper, and its intensity doesn't depend on latitude, but it also penetrates through glass, plastic, and clothing. This means we are most exposed to UVB on sunny summer days, while UVA affects us all year round, even on very cloudy winter days (or even when hidden under an parasol on the beach!).

effects of UVA and UVB radiation on the skin

Thanks to UV radiation and the sun, our bodies begin to synthesize vitamin D, our mood improves, and a nice tan can appear. Unfortunately, this is where the pros end, and a longer list of cons begins. From a medical standpoint, there is no reason to sunbathe. A "nice tan" is actually the result of unhealthy skin damage. UVB radiation causes burns, erythema, and hyperpigmentation. UVA, on the other hand, causes photoaging of the skin through damage to DNA - accelerating the formation of wrinkles and causing skin sagging (damage you'll notice after years of excessive tanning). At its worst, UV radiation leads to (often) fatal skin cancer, especially among fair-skinned people. And if you're worried about vitamin D deficiency, frying in the sun will do more damage to you and will most likely not improve your vitamin D levels at all.

💡 Did you know that light-skinned people can only safely spend a few minutes in the sun in the summer? Applying an SPF cream extends that time to several hours! You can learn more in our sunbathing calculator.

If you want to have healthy and young-looking skin for as long as possible and not develop skin cancer, you should use SPF sunscreen all year round (and don't forget about vitamin D supplementation: use our vitamin D calculator). But which sunscreen should you choose so that you're protected?

Which sunscreen to choose?

On the market, we can find sunscreens with labels from SPF 5 to SPF 50. What are these mysterious abbreviations? SPF, which stands for sun protection factor, is the factor of protection against UVBs. Its value indicates the amount of sun radiation our skin can withstand when a given filter protects it before causing erythema. For example, SPF 20 protects us until we expose our skin to 20 times more radiation than needed to cause erythema. We recommend using creams with SPF of at least 30.

Not all commercially available creams also protect against UVA. In the USA, choose sunscreens with the label "broad spectrum". These (if used correctly) will protect you from both UVA and UVB radiation. The markings can be different in other countries, but all creams that protect from UVA will have that information on the label. Anywhere you are, buy creams that protect against both UVA and UVB.

Did you know that adults who experienced frequent sunburns as children are much more likely to get skin cancer? Make sure that your children use sunscreen, wear protective clothing and a hat whenever they go outside to play.

How much sunscreen should we apply?

On average, we should apply 2 mg of cream per cm² of the body. This means that we should apply cream squeezed over the entire length of our index and middle fingers for the face alone. This is obviously a very inaccurate measurement, especially remembering that each cream has a slightly different density. But it's probably still a lot more than you would normally apply!

We should put the same amount of cream on the rest of the body (2 mg/cm²), but unfortunately, we don't have a good recommendation for measuring it. On average, you should apply about 1.2 fl oz of cream. The calculator will tell you more precisely how much you should put on your arms and legs.

Enjoy summer safely!

To help keep you and your loved ones safe, inspired by the recommendations of the World Health Organization (WHO), we've put together some advice for summer and sunny days:

  • Spend as little time in the sun as possible between 10 am and 4 pm. On vacation, try to choose indoor or shaded activities during the hours with the highest intensity of sunlight. Head for walks and the beach in the mornings or evenings.

  • Cover your skin with clothing. 👚👖 In summer, choose loose but densely woven fabrics and clothes with long sleeves and legs. Pick up clothes made of linen or cotton - in these, you won't overheat and they will protect your skin from burns. You also won't have to use as much sunscreen.

  • Remember to cover your head: our hat size calculator can help you. 👒

  • Use a sunscreen that protects against both UVB and UVA rays.

  • Apply sunscreen at home before going to the beach/on a walk. You'll apply it more thoroughly at home, and it will have time to absorb, so you'll be protected from the beginning.

  • Reapply the cream every two hours or so - more often if you go in the water. ⏲️ The active ingredients in creams will wear off after reflecting or absorbing a certain amount of radiation and will no longer be effective.

  • Protect your eyes! 😎 Strong radiation can damage not only our skin but also our eyesight. In addition to protecting your skin with SPF creams, get yourself some good sunglasses (no, those cheap ones from the beach market won't change anything).

  • Do not irritate burns. In the event of a burn, shade yourself from the sun and protect the damaged area until it heals.

  • Always carry a bottle of water and regularly hydrate: our water intake calculator can help you. 💧 Use our chill drink calculator to find out how long a particular beverage should take to cool to its optimal hydration temperature.

In special cases:

  • A few weeks after COVID-19 recovery or vaccine, avoid the sun. The skin may be weakened or have some lesions, making it more susceptible to developing cancer.
  • Avoid sunbathing while pregnant. 🤰 Pregnant women have more sensitive skin and are more likely to get burned. In summer, try to shelter your belly under your clothes and avoid overheating your body.

How to use the calculator?

Our calculator will tell you how much sunscreen you will need for a given number of days. And you will be surprised how much you should use (or how little?).

  1. Do you want to calculate the amount of sunscreen needed for your face or your body?
  • If you chose body - input your weight and height.

  • If you chose face - with a measuring tape, measure your face's width (from ear to ear) and height (from the hairline in the middle of your forehead to your chin) and enter the numbers into the calculator.

  1. How many days are you going away for? How long do you need the cream for?
  2. How many hours a day will you be in the sun?
  3. How large a container of sunscreen will you take with you? Remember, less volume means more plastic packaging.
  4. If you chose body: Will you cover your body? If so, will you wear a short-sleeved or long-sleeved top? Will you wear a long skirt or trousers?

When you answer these questions, our calculator will tell you the amount of cream you need for your trip in seconds. But, wait a minute - this is the amount of cream just for you! If you are traveling with a partner or teenage children, you'll need to run the calculations again!

Now you know how much sunscreen you need to take on your next trip and what to do to safely enjoy the sun. But if you think you can't live without a tan, instead of frying on the beach, choose fake tan!

FAQ

How do I calculate how much sunscreen I need for my body?

The general requirement of various body parts is:

  1. 2.9 ml for each arm.
  2. 5.8 ml for each leg.
  3. 12 ml for the torso, front, and back.
  4. 0.35 ml for the face.
  5. Sum them all together.
  6. The result is the amount of sunscreen you need for your entire body, including your face.
  7. It is approximately 29.75 ml.

Remember, this is a generalization. Your particular need may vary, and for that, we suggest using a tool like our sunscreen calculator for accuracy.

How long does 1.7 oz of sunscreen last?

1.7 ounces of sunscreen should last about 8-9 weeks for the face only and 1- 2 days for the body.

The factors on which the amount may vary are the number of days and the duration you will be in the sun, along with your body height, weight, and face size.

How many bottles of sunscreen do I need for 1 week?

For a week's vacation during which you remain in the sun for 3 hours a day, you will need 1.5 bottles of 5 fl oz / 150 ml. So we suggest taking 2 bottles to be safe, as the amount of sunscreen also changes with your height and weight.

Does SPF 30 mean 30 minutes?

No, it doesn't. We understand why you may think so, but that is not what the numbers mean. This number is to give you an approximate value of how long you have before your skin may start to burn.

So, for instance, if your skin burns after being in the sun for 2 minutes, applying SPF 30 sunscreen would increase the time to 60 minutes. Here is how:

Protection time = SPF × Burning time

Protection time = 30 × 2 minutes

Protection time = 60 minutes

Julia Żuławińska and Aleksandra Zając, MD
Pale, dark-skinned, or somewhere in the middle - no matter your skintone or sunbathing goals for this summer, this calculator will help you figure out how much sunscreen you should use to keep yourself safe from the dangers of UV rays, and how many containers you need to take for your holiday. 🏖️
Let's calculate the amount of sunscreen for your....
body
Your weight
lb
Your height
ft
in
How many days will you be in the sun?
days
How long you will stay in the sun each day?
hrs
Sunscreen package
5 fl oz / 150 ml
Clothes besides a swimsuit?
No
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