We created this sunscreen calculator to help determine the appropriate amount of sunscreen needed for effective protection against harmful UV rays by considering BSA, sun exposure time, and the SPF of the sunscreen.
Let’s say you’re planning a beach day. A sunscreen calculator might consider:
- Your height and weight to estimate body surface area
- The duration of your beach visit
- The SPF of your sunscreen
- The intensity of UV radiation at your location
Sunscreen Calculator
| Height (cm) | Weight (kg) | BSA (m²) | Single Application (ml) | Daily Usage (3 applications) | 2-Week Usage (ml) |
|---|---|---|---|---|---|
| 160 | 60 | 1.63 | 32.6 | 97.8 | 1,369 |
| 175 | 75 | 1.91 | 38.2 | 114.6 | 1,604 |
| 180 | 80 | 2.00 | 40.0 | 120.0 | 1,680 |
| 165 | 55 | 1.60 | 32.0 | 96.0 | 1,344 |
| 190 | 90 | 2.19 | 43.8 | 131.4 | 1,840 |
Sunscreen Calculation Formula
The formula for calculating sunscreen usage is:
Amount of sunscreen (in ml) = Body Surface Area (in cm²) × 2 mg/cm²
This formula is based on the standard recommendation of applying 2 mg of sunscreen per square centimeter of skin.
For an average adult with a body surface area of 1.8 m² (18,000 cm²): 18,000 cm² × 2 mg/cm² = 36,000 mg = 36 ml of sunscreen
How do you calculate how much sunscreen you need?
To calculate your sunscreen needs:
- Estimate your body surface area (BSA): Use the Mosteller formula: BSA (m²) = √[(Height (cm) × Weight (kg)) / 3600]
- Convert BSA to square centimeters: Multiply by 10,000
- Apply the 2 mg/cm² rule: Multiply your BSA in cm² by 2
- Convert mg to ml: Divide the result by 1000
For a person 170 cm tall weighing 70 kg:
BSA = √[(170 × 70) / 3600] = 1.81 m²
1.81 × 10,000 = 18,100 cm²
18,100 × 2 = 36,200 mg
36,200 / 1000 = 36.2 ml
This person should apply approximately 36 ml of sunscreen for full-body coverage.
Why do we need sunscreen?
Sunscreen is crucial for protecting our skin from the harmful effects of UV radiation, including:
- Sunburn: Immediate reddening and pain in the skin
- Premature aging: Wrinkles, age spots, and loss of skin elasticity
- Skin cancer: Increased risk of melanoma and non-melanoma skin cancers
- Immunosuppression: Weakening of the skin’s immune function
- Eye damage: Increased risk of cataracts and macular degeneration
How much sunscreen for 2 weeks?
- Assuming 3 applications per day: 36 ml × 3 = 108 ml daily
- For 2 weeks: 108 ml × 14 = 1,512 ml or about 1.5 liters
To calculate sunscreen needs for a two-week period:
Determine daily usage (as calculated earlier)
Multiply by the number of applications per day (typically 2-3)
Multiply by 14 days
This amount ensures proper coverage for a two-week period, but actual usage may vary based on factors like activities and sun exposure.
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