The Sunbathing Calculator shows how much time you can safely spend in the sun, depending on the sunlight intensity, your skin type, and what SPF you're planning to apply.

Sure, you always remember to put on cream whenever you're going surfing, skiing or trekking, but are you sure an SPF 10 is enough? Sunburns hurt, the peeling skin looks far from sexy, but more importantly, every time you get a sunburn, the risk of getting skin cancer in the future rises. Even if you're a vitamin D junkie, enjoy the sun safely! Read on to learn how to tan without damaging the skin, why it's important to know the UV Index for tanning, and what SPF to use. Unless you want to see how long it takes to get sunburned.

How to tan safely?

The World Health Organization's precautions on how to tan safely are a good point to start. In short, you need to:

  • Limit the time spent outside between 10 a.m. and 4 p.m.
  • Watch for the UV index, which represents the sunlight intensity.
  • Use shade wisely - remember that umbrellas and trees don't protect you completely!
  • Wear protective clothing - especially loose fitting, made of tightly woven fabric. Good quality sunglasses and a wide-brimmed hat are not just stylish accessories - in direct sunlight, they are a must!
  • Use sunscreen - cover all exposed skin by a thick layer of cream and reapply it after any activity that might wear it off. Scroll down to learn what SPF to use for your skin type.
  • Avoid sunlamps and tanning parlors!

Our extra tips:

  • Stay hydrated - find out how much water you exactly need using water intake calculator.
  • Remember the shadow rule: watch your shadow – if it's short, you should seek shade! If it's getting longer, you're less likely to get sunburned.
  • Watch the ingredients of your cream - some substances, like oxybenzone and octinoxate, have recently been banned in Hawaii, due to their harmful impact on the ecosystem. It hasn't been proved that they can be harmful to humans after applying to the skin in sunbathing quantities, but let's be mindful of the environment and avoid them anyway.

What do UV Index and tanning have in common?

The Ultraviolet Index, or UVI for short, represents the risk of sunburn due to UV radiation and corresponds to the intensity of the sunlight. It's described by a scale from 0 to 11+. Check out the current UV index in your exact location using the fantastic sunburn map. You can also assess it very roughly just by looking outside:

UVI Intensity Circumstances
0 none at night
1-2 low on a very cloudy day, or a cloudy day in winter
3-5 moderate on a partly cloudy day in spring or autumn
6-7 high on a sunny day in spring or autumn
8-10 very high on a very sunny day in the summer
11+ extreme very sunny on high altitudes and/or in the tropical zone

The table presents international color codes approved by the World Health Organization.

It's important to mention that ultraviolet radiation is decreased by the thickness of atmosphere it has to pass through. Due to that, the intensity of UV rays increases with altitude, and is greatest during summer months in the tropical zone, at noon. It's substantially lower from autumn to spring, in the mornings and afternoons, and further from the equator. Additionally, ground reflection increases the radiation exposure dramatically - consider extra precautions if you plan to be in or on the water, snow or any other reflective ground!

Good UV Index for tanning

It is important to remember that, in practice, no UV index is truly good for tanning. The NHS warns that a “healthy tan” does not really exist, spending long periods of time in direct sunlight is not recommended, no matter the UV index value, as any tan can increase the risk of developing skin cancer.

Here is a short guide explaining what precautions should be taken to stay healthy based on the UV index:

1. UV Index 0 - 2

  • Low exposure level
  • Average time it takes to burn: 60 minutes
  • Recommended actions: SPF 30+ sunscreen, sunglasses.

2. UV Index 3 - 5

  • Moderate exposure level
  • Average time it takes to burn: 45 minutes
  • Recommended actions: SPF 30+ sunscreen every 2 hours, hat, sunglasses, seek shade between 10AM and 4PM.

3. UV Index 6 - 7

  • High exposure level
  • Average time it takes to burn: 30 minutes
  • Recommended actions: SPF 30+ sunscreen every 2 hours, wide-brimmed hat, sunglasses, seek shade between 10AM and 4PM, wear long sleeves and pants if comfortable.

4. UV Index 8 - 10

  • Very high exposure level
  • Average time it takes to burn: 15 - 25 minutes
  • Recommended actions: SPF 30+ sunscreen every 2 hours, wide-brimmed hat, sunglasses, seek shade between 10AM and 4PM, wear long sleeves and pants if comfortable, limit time outdoors to a minimum.

5. 11+ UV Index

  • Extreme exposure level
  • Average time it takes to burn: 10 minutes
  • Recommended actions: SPF 30+ sunscreen every 2 hours, wide-brimmed hat, sunglasses, seek shade between 10AM and 4PM, wear long sleeves and pants if comfortable, limit time outdoors to a minimum.

Why are the UV rays dangerous?

The ultraviolet radiation is divided into three ranges, depending on its wavelength:

  • UVA - the longest waves (wavelength 315–400 nm) - they penetrate deep into the skin and cause skin aging. Watch out, they don't give you the sexy tan, but they get through glass, so you should protect your skin even when you're inside.
  • UVB - the medium waves (wavelength 280–315 nm) - they stimulate melanocytes in the skin. Melanocytes are responsible for the production of melanin, the skin pigment that makes you look tanned, but can also mutate into cancer cells and lead to melanoma if they're overstimulated. The UVB rays are also the reason of sunburns.
  • UVC - the shortest waves (wavelength 100–280 nm) - luckily, they are absorbed in the atmosphere.

If you have one of the lower skin phototypes, you're probably familiar with the typical symptoms of a sunburn: redness, itchiness, blisters, and skin peeling off. Don't try to act tough and ignore the risks. Every intense sunbathing episode brings you closer to hyperpigmentation and skin aging, and overexposure can lead to skin cancer.

What's my skin phototype?

The natural sensitivity to sunlight depends on the skin's pigmentation level. That means it's directly related to its color. The phototypes are described by the Fitzpatrick scale:

  • type I - very pale skin, doesn't tan, always burns
  • type II - fair skin, tans a little, burns easily
  • type III - medium skin, tans easily after an initial burn
  • type IV - light brown skin, tans very easily, burns minimally
  • type V - dark brown skin, tans darkly, burns very rarely
  • type VI - black skin, always darkens, never burns

Remember that babies' and children's skin is always more sensitive, so if you're using our sunscreen calculator to estimate safe outside time for a child, set their skin type to a lower number.

Using the Sunbathing Calculator

Before you hit the beach, make sure you know how long you can safely stay in the sun.

  1. Input the sunlight intensity - choose one of the options in the first list or enter the exact UV Index value in the advanced mode.
  2. Choose the altitude - if you're on a beach, it's safe to say you're not higher than 1000 meters 😎
  3. Check if you're going to be on a reflective ground - swimming also counts, as long as there's any exposed skin over the water surface!
  4. Choose your skin phototype.
  5. Enter the SPF of the sunblock you're going to use. If you don't care about protection, leave 1 in this field.
  6. The estimated time you can spend outside is displayed in the last box 🌴

Now you're ready to head straight to the beach!

Reverse calculation - what SPF to use?

The abbreviation SPF, that you often see on sun cream packaging, stands for Sun Protection Factor and is a parameter that indicates how much of the UVB rays the sun block product absorbs.

You can use the Sunbathing Calculator to check what SPF to apply! To do so, leave the SPF of the cream field empty, but enter the maximum time you're planning to spend in the sun. The calculator will estimate what cream you should put on. If the result ends up in between the standard factors, always pick the cream with a higher number on it - it's better to be safe than sorry!

According to scientific research, it's best to apply sun protection cream twice: once 15-30 minutes before going outside, and once 15-30 minutes after the exposure begins. After that, you only need to reapply the sunscreen after swimming, sweating, or any activity that might rub the protection off.

The Sunbathing Calculator was created by Małgorzata Koperska MD, an Omni Calculator physician.

Małgorzata Koperska, MD
Sunlight intensity
moderate - partly cloudy
up to 1000 m (3,280 ft)
Are you on water or snow?
type III - medium skin
SPF of the cream
Maximum time outside
Remember to reapply sunscreen every two hours for optimal protection.
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