Sunscreen Calculator

By Julia Żuławińska and Aleksandra Zając, MD
Last updated: Aug 18, 2021

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. ☀️☀️

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). 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. 👒

  • 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. 💧 Use our beverage cooling 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!

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
People also viewed…

Roll length

This roll length calculator will help you find the length of any rectangular sheet which has been rolled up!

Steps to calories

Steps to calories calculator helps you to estimate the total amount to calories burned while walking.

Test grade

With this test grade calculator you'll easily find out the test percentage score and grade.

Time duration

The time duration calculator is a tool that allows you to find the time duration between two times. It supports the 12- and 24-hour time formats.
main background