Your sunscreen plan for today.
Set the UV index from your weather app, the phototype that matches how your skin reacts to strong sun, and the hours you plan to be outside. You get the amount in grams, the times to reapply, a 24 hour ring of the day and a card you can share.
Four numbers make today's plan.
Take the UV index from a weather app for your location, pick the phototype that matches how your skin reacts to strong sun, and set the hours you plan to be outside. Everything updates while you move the slider, and nothing is stored.
Moderate on the WHO scale, where protection is recommended from UV 3.
How your skin reacts to the first strong sun of the year, not how it looks.
Every one of these numbers is measured at 2 mg per square centimetre.
6 hours outdoors.
Water and a towel take the film off, whatever the label claims.
UV 5
Moderate on the WHO UV index
Face and neck, in grams
1.2 g is about a quarter of a teaspoon, or two finger lengths squeezed along your index and middle finger. That is the 2 mg per square centimetre every SPF number is tested at.
| Each arm | about 3 g |
|---|---|
| Each leg | about 6 g |
| Whole body | 30 to 35 g |
A level teaspoon holds about 5 g, so a whole body takes six to seven of them.
How it works.
- Set the UV index from your weather app, then pick the phototype that matches how your skin reacts to the first strong sun of the year.
- Choose the product SPF, the hours you plan to be outdoors and whether you swim or sweat heavily.
- Read the amount in grams, the reapplication times and the 24 hour ring, then save the card or send it to whoever is coming with you.
What the UV index counts
The UV index is a forecast of how strong solar ultraviolet radiation is at ground level, usually given for the middle of the day. The WHO scale runs upwards in five steps: 0 to 2 low, 3 to 5 moderate, 6 to 7 high, 8 to 10 very high, and 11 or more extreme. Protection is advised from 3 upwards. The number climbs with the height of the sun, so it peaks in the hours around solar noon, and it rises with altitude by roughly 10 percent for every 1000 metres. Surfaces add to it: fresh snow reflects up to 80 percent of UV back at you, dry sand about 15 percent and water about 10 percent, which is why a seat in the shade beside water is not the same as shade under a tree.
Why the amount decides the number
Every SPF on a label is measured at 2 mg of product per square centimetre of skin. For a face and neck that is about 1.2 g, roughly a quarter of a teaspoon or two finger lengths squeezed along the index and middle finger; for a whole adult body it is 30 to 35 g, six to seven teaspoons. Studies of everyday use find that most people apply a quarter to a half of that, and the protection drops away faster than the amount does. The steps between the numbers are small: SPF 15 filters about 93 percent of UVB, SPF 30 about 97 percent and SPF 50 about 98 percent. Reapply every 2 hours outdoors, and again straight after swimming or towelling. How much sunscreen the face needs shows the measure on a hand, and mineral or chemical filters explains what does the work.
What this tool is not
It is not a measurement of your skin, and it does not say how long you may stay in the sun: skin, cloud, surface and the amount you apply all move that answer, so no calculator should promise it. Phototypes I to VI describe how skin reacts to the first strong sun of the year, not ethnicity. SPF describes UVB only, so look for the UVA symbol in a circle or a PA rating for the rest. Sunscreen is one layer: shade around the middle of the day, a shirt, a hat and sunglasses are the others. Some medication and some skincare actives raise sun sensitivity, which is a question for a pharmacist or a doctor, and skin that already feels raw belongs with the barrier repair plan before any acid.
Frequently asked.
Does a higher SPF let me stay out longer?
No. The number describes how much UVB the film filters when it is applied at 2 mg per square centimetre, not extra hours in the sun: SPF 30 filters about 97 percent and SPF 50 about 98 percent. Both need the same fresh layer every 2 hours outdoors.
How do I measure 1.2 g on my face?
Squeeze the product along your index finger and your middle finger, from the base to the tip, and use both lengths on face and neck. That is about a quarter of a teaspoon, and a whole adult body takes 30 to 35 g.
Does water resistance replace reapplying?
No. Water resistance is tested in 20 minute cycles in water, and a label may claim 40 or 80 minutes of it, which describes the film in water rather than the sun above it. Reapply straight after swimming or after a towel, whatever the clock says.
Do I need sunscreen at UV 2, or indoors behind glass?
At UV 0 to 2 most people need no extra protection outdoors. Window glass stops nearly all UVB but lets a share of UVA through, so a desk at a sunny window for hours a day is worth a layer.
What does the phototype change in the plan?
It changes the advice, not the amount: 2 mg per square centimetre is the same for every skin. Phototype I and II skin reacts fastest, so shade and clothing carry more of the load, while phototype V and VI skin burns rarely and still shows pigment changes from UV.
Does the planner store or send anything?
No. Every number is worked out in your browser, nothing is saved and nothing is uploaded, and the share card is drawn on a canvas on your own device.
Guides behind this tool
Skincare
How much sunscreen a face needs: the 2 mg per square centimetre rule
Ingredients
Mineral or chemical sunscreen filters: how they work
Skincare
A damaged skin barrier: signs, causes and repairMore tools
The SPF Day Planner turns a UV index, a phototype and an outdoor window into an amount and a set of times. It does not measure your skin, it does not say how long you may stay in the sun, and it cannot judge moles, sun damage or a reaction to medication. This page is for general information and does not replace advice from a dermatologist, physician or qualified practitioner.