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Sunbathing Calculator

Table of contents

How to tan safely?What do UV Index and tanning have in common?Good UV Index for tanningWhy are the UV rays dangerous?What's my skin phototype?Using the sunbathing calculatorReverse calculation — what SPF to use?FAQs

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, and the peeling skin looks far from sexy, but more importantly, every time you get sunburned, 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 essential to know the UV Index for tanning, how to use our sunbathing calculator 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 with 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.
  • 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 proven that they can be harmful to humans after being applied to the skin in sunbathing quantities, but let's be mindful of the environment and avoid them anyway.

Would you like to check out our edpi calculator? It finds your effective mouse sensitivity so you can easily compare it to your friends.

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 on a scale from 0 to 11+. Check out the current UV index in your exact location using the fantastic UV index search from the EPA. You can also assess it very roughly just by looking outside:






At night



On a very cloudy day or a cloudy day in winter



On a partly cloudy day in spring or autumn



On a sunny day in spring or autumn


Very high

On a very sunny day in the summer



Very sunny on high altitudes and/or in the tropical zone

The international color codes approved by the World Health Organization that match the above table are:

  • Low: green;
  • Moderate: yellow;
  • High: orange;
  • Very high: red; and
  • Extreme: purple.

It's important to mention that ultraviolet radiation is decreased by the thickness of the 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 radiation exposure dramatically — consider extra precautions if you plan to be in or on the water, snow, or any other reflective ground!

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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 you should take 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 and 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, and seek shade between 10 am and 4 pm.

3. UV Index 6-7;

  • High exposure level;
  • Average time it takes to burn: 30 minutes;
  • Recommended actions: SPF 30+ sunscreen every 2 hours, a wide-brimmed hat, sunglasses, seek shade between 10 am and 4 pm, and 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, a wide-brimmed hat, sunglasses, seek shade between 10 am and 4 pm, wear long sleeves and pants if comfortable, and 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, a wide-brimmed hat, sunglasses, seek shade between 10 am and 4 pm, wear long sleeves and pants if comfortable, and 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 a sexy tan, but they get through the 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 they can also mutate into cancer cells and lead to melanoma if they're overstimulated. The UVB rays are also the reason for 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 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.

Let's take our minds off sunbathing and try out the grade calculator!

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; and
  • Type VI — black skin, always darkens, never burns.

Remember that the skin of children and babies 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 hitting the beach, ensure you know how long you can safely stay in the sun.

  1. Select the sunlight intensity you anticipated to be under — pick one of the dropdown options in the Sunlight intensity variable of our sunbathing calculator. Choose the last dropdown option to enter a custom UV index or the exact UV index value forecasted for your location.
  2. Choose your 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 like water or snow — swimming also counts, as long as there's any exposed skin over the surface of the water.
  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.

Reverse calculation — what SPF to use?

The abbreviation SPF, which 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 sunblock 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 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.


How long will it take to tan at a UV index of 7?

You can stay safely in the UV index of 7 for approximately 30 minutes (2–70 minutes) before you get sunburned. The exact value depends on the altitude, the presence of water/snow, your skin type, and the use of sunscreen.

How do I calculate time for sunbathing?

To assess the maximum time for sunbathing (before you get burned), consider:

  1. The sunlight intensity;
  2. The altitude;
  3. The UV index of your location;
  4. Whether you're on water or snow;
  5. Your skin type;
  6. Whether you're using sunscreen and what SPF you're using.

Then, use the formula:

max time = (skin type × SPF)/(UV index × altitude × water-snow factor)

Try our sunbathing calculator for more information!

What is the best UV index for tanning?

It is recommended to only stay in the sun on purpose when the UV index is low to moderate — meaning "up to 5". You can minimize the risk of skin damage by avoiding the higher (6+) sunlight intensities. Even if you want to get a tan, remember to use proper sunscreen.

How do I use SPF to tan?

When tanning, use SPF as usual:

  1. Apply a decent amount — 2 mg of cream per 1 cm² of the skin.
  2. Cover your whole body and face (don't forget the lips and ears).
  3. Re-apply every two hours, and after swimming, sweating or rubbing it off.
  4. Aim for SPF 30 and higher.
  5. Apply the first layer 20 minutes before going into the sun.

Remember to reapply the sunscreen after swimming, sweating, and rubbing it off or every two hours for optimal protection.

Make sure to check how much sunscreen to take with you on vacation, too! 

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