# Sunscreen Calculator

URL: https://speedycalculator.com/calculators/everyday-life/sunscreen/
Last updated: 2026-10-25

> The sunscreen calculator works out how much sunscreen you need for a full-body application, how many times to reapply each day, and how many bottles to pack for a holiday.

## Inputs

- Height (cm, in, ft)
- Weight (kg, lb, g)
- Skin exposed
- Hours in the sun per day
- Days
- Bottle size

## Results

- Body surface area
- One application
- Applications per day
- Sunscreen for the trip
- Bottles to pack

## Formula

```
Body surface area (Mosteller) = √(height cm × weight kg ÷ 3,600)
One application = 2 mg/cm² × exposed skin area (≈ 30 mL for an adult in swimwear)
Applications per day = ceil(hours in the sun ÷ 2)
```

## Explanation

Sunscreen only gives the SPF on the label when applied at 2 mg per square centimetre – about a shot glass (30 mL) for an adult's whole body. Most people apply a quarter to half of that. Reapply at least every two hours and after swimming or sweating.

### How to use the Sunscreen Calculator

- **Height**
- **Weight**
- **Skin exposed**
- **Hours in the sun per day**
- **Days**
- **Bottle size**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter your height and weight, the share of skin exposed, the hours you spend in the sun each day, the number of days and your bottle size.

### Tips

- Use the amounts printed on the product (ml, sheets, applications) where available.
- Count everyone in the household who shares the product.
- Buy a little extra so you never run out unexpectedly.
- Small daily habits add up – check the yearly figures for the real impact.

### Common mistakes to avoid

- Forgetting that hot water costs energy as well as water.
- Underestimating how much sunscreen a full application needs.
- Comparing pack prices without checking the size of each pack.

### Inputs explained

FieldWhat to enterHeightUnits: cm, in, ftWeightUnits: kg, lb, gSkin exposedChoose one: Swimwear (≈ 85%), Shorts and T-shirt (≈ 50%), Face, neck, arms (≈ 20%), Face only (≈ 5%)Hours in the sun per dayA numberDaysA numberBottle sizeChoose one: 50 mL / 1.7 fl oz, 100 mL / 3.4 fl oz, 150 mL / 5 fl oz, 200 mL / 6.8 fl oz …

### What each result means

- **Body surface area** = sqrt([Height]×100×[Weight]÷3600)
- **One application** = [Body surface area]×10000×[Skin exposed]×2÷1000÷1000×1e-3
- **Applications per day** = max(ceil([Hours in the sun per day]÷2 - 0.000001), 1)
- **Sunscreen for the trip** = [One application]×[Applications per day]×[Days]
- **Bottles to pack** = ceil([Sunscreen for the trip]÷[Bottle size] - 0.000001)

### Example values

How the main result changes when **Height** changes and everything else stays at the example values above:

Height (cm)Sunscreen for the trip (mL)85459127.5562170649212.5726255795340918

## Worked example

Inputs — Height: 170 cm; Weight: 70 kg; Skin exposed: Swimwear (≈ 85%); Hours in the sun per day: 6; Days: 7; Bottle size: 100 mL / 3.4 fl oz.

Results — Body surface area = 1.82 m²; One application = 30.9 mL; Applications per day = 3; **Sunscreen for the trip = 649 mL**; Bottles to pack = 7.

## FAQ

**How much sunscreen should I use?**
About 30 mL (a shot glass) for an adult's whole body, or half a teaspoon for the face and neck.

**How often should I reapply?**
At least every two hours, and immediately after swimming, sweating or towelling.

**Does SPF 50 mean I can apply less?**
No – using half the amount gives far less protection than the SPF number suggests.

**What formula does the Sunscreen Calculator use?**
Body surface area (Mosteller) = √(height cm × weight kg ÷ 3,600).


## Sources

- [American Academy of Dermatology – How to apply sunscreen](https://www.aad.org/public/everyday-care/sun-protection/shade-clothing-sunscreen/how-to-apply-sunscreen)