Sunscreen Calculator: How Much You Need & Bottles to Pack

Sunscreen Calculator

How much you need and how many bottles to pack

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Sunscreen SPF ratings are tested at an application rate of 2 mg of cream per cm² of skin — far more than most people actually apply. For an average adult, that works out to roughly 30 mL (about 6 teaspoons) to cover the whole body once.

Face-only coverage uses the "two finger" rule — a strip of cream along your index and middle fingers, about 0.35 mL. Reapply every 2 hours, and immediately after swimming or heavy sweating.

Coverage

Full Body Face Only

Weight

Height

Used to estimate your body surface area — taller/heavier bodies need proportionally more sunscreen.

Clothing Coverage

Less exposed skin means less sunscreen needed for full-body coverage.

Applications per Day

Every 2 hours of sun exposure is the standard reapplication interval.

Days Away

Bottle Size

☀️ Your Result

Bottles to Pack

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Fill in the fields above to calculate

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Per Application

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Total Needed

Calculation

Most people apply far less sunscreen than the amount its SPF rating was actually tested at, this calculator works out how much you really need per application, and how many bottles to pack for a trip, based on your body size and the dermatological application standard.

How to use this sunscreen calculator

Choose Coverage: Full Body or Face Only.
For full body, enter your Weight, Height, and Clothing Coverage level.
Enter Applications per Day and Days Away.
Choose a Bottle Size, or enter a custom size.
Read your Per Application amount, Total Needed, and Bottles to Pack.

What this calculator does

Sunscreen SPF ratings are tested at an application rate of 2 mg of cream per cm² of skin, far more than most people actually apply in practice. For an average adult, that works out to roughly 30 mL (about 6 teaspoons) to cover the whole body once. This calculator estimates your body surface area from height and weight, adjusts for how much skin your clothing actually exposes, and multiplies out by your trip length and reapplication frequency.

Per-Application Amount ≈ Body Surface Area × 2 mg/cm² × Clothing Coverage Factor
Total Needed = Per-Application Amount × Applications per Day × Days Away

Why clothing coverage changes the amount

Less exposed skin means less sunscreen is needed for full coverage, someone in swimwear needs to cover far more surface area than someone in long sleeves and trousers. This calculator’s Clothing Coverage setting scales the estimate down accordingly rather than assuming full-body exposure regardless of what you’re wearing.

The face-only “two finger” rule

For face-only coverage, dermatologists commonly reference the “two finger” rule, a strip of cream applied along the length of your index and middle fingers, roughly 0.35 mL, which this calculator uses as the baseline for face-only estimates.

Reapplication matters as much as the initial amount

Every 2 hours of sun exposure is the standard reapplication interval, and immediately after swimming or heavy sweating regardless of how much time has passed. This calculator’s Applications per Day field lets you plan for realistic reapplication frequency rather than a single morning application.

Frequently asked questions

Why do I need so much more sunscreen than I probably use?

SPF ratings are tested at 2 mg per cm² of skin, an amount most people significantly under-apply in real life. Under-applying doesn’t just waste the bottle faster, it also means you’re getting meaningfully less sun protection than the SPF number suggests.

How often should I reapply sunscreen?

Every 2 hours of sun exposure is the standard interval, and immediately after swimming or heavy sweating regardless of how recently you applied it.