How much sunscreen to pack for a Bahamas trip: calculator

How the planner works

One coat. The American Academy of Dermatology says most adults need about 1 ounce of sunscreen, roughly a shot glass, to cover the body. The calculator uses 1 US fluid ounce, about 29.6 ml, per adult per full application.

Children. Each child is counted at half an adult's amount, about 14.8 ml a coat. That is our own estimate for smaller bodies, not an official figure, and an older child may need nearly as much as an adult. For babies under six months, the FDA advises asking a doctor before applying sunscreen.

Coats a day. The academy advises reapplying every two hours and straight after swimming or sweating. The calculator counts:

• a first coat as you go out;
• another at the two-hour mark, the four-hour mark and so on, as long as you are still outside;
• one more after each swim;
• never more than one an hour: the total is capped at your hours outside, rounded up, plus the first coat.

Spend no time outside and the result is zero.

Totals. The party's amount per coat is multiplied by the coats a day and the days of the trip, then shown in millilitres, fluid ounces, 3 oz travel bottles and 6 oz bottles, rounded up to whole bottles.

ml per coat   = adults × 29.6 + children × 14.8
coats a day   = 1 + one at each 2-hour mark while outside + swims
                (at most: hours outside, rounded up, + 1)
ml a day      = ml per coat × coats a day
trip total    = ml a day × days
3 oz bottles  = trip total ÷ 88.7 ml, rounded up
6 oz bottles  = trip total ÷ 177.4 ml, rounded up

The calculator accepts up to 14 hours outside and up to 8 swims a day.

Worked example

The calculator opens with two adults, no children, a 7-day trip, 6 hours outside a day and 2 swims.

• Coats a day: a first coat, one at two hours and one at four hours, plus one after each of the 2 swims, makes 5. The cap would be 7, so it does not apply.
• Per coat: 2 adults × 29.57 ml = about 59.1 ml.
• Per day: 5 coats × 59.1 ml = about 296 ml.
• For the trip: 296 ml × 7 days = about 2,070 ml, or 70 fl oz.
• Bottles: 24 travel bottles of 3 oz, or 12 bottles of 6 oz.

That is a lot of liquid, and better known before you pack than halfway through the week. Add two children to the same plan and it rises to about 444 ml a day and 3,105 ml (105 fl oz) for the week: 35 travel bottles or 18 of the larger size.

What it can't tell you

Anything about your skin or health. The calculator knows nothing about skin type, skin conditions or medicines that make you more sensitive to the sun. If any of those apply, or for babies and young children, ask a pharmacist or doctor which product and how much.

Which product to use. The academy recommends a broad-spectrum, water-resistant sunscreen with SPF 30 or higher. Water-resistant labels must say whether the product lasts 40 or 80 minutes, so follow the label if it asks for more coats.

How much you sweat. Only swims are counted; a hot hike or a sweaty day on deck calls for extra coats.

How much skin you cover. The shot-glass figure assumes swimwear. A rash guard and a hat reduce the skin you need to cover, shade cuts the sun that reaches you, and the FDA advises covering up and limiting time in the sun, especially between 10 am and 2 pm. Our guide to snorkelling Bahamian reefs safely has more on protecting yourself in the water.

Your airport's rules. The 3 oz bottles fit under the US hand-luggage limit for liquids; other airports set their own, so check before you fly. The packing list planner covers everything else.

Sources

• American Academy of Dermatology: How to apply sunscreen
• US Food and Drug Administration: Sunscreen, how to help protect your skin from the sun
• TSA: Liquids, aerosols and gels rule

Frequently asked questions

How much sunscreen does one person need for a week in the Bahamas?

With 6 hours outside and 2 swims a day, the calculator gives one adult about 148 ml a day and 1,035 ml, or 35 fl oz, for a 7-day trip. That is 12 travel bottles of 3 oz or 6 bottles of 6 oz.

Can I take sunscreen in my hand luggage?

For flights screened under US rules, yes, in containers of 3.4 oz (100 ml) or less that fit in your one quart-sized bag of liquids. Larger bottles go in checked luggage. Other airports have their own rules, so check with yours.

How much sunscreen does a child need?

The calculator counts a child at half an adult's amount, which is our own estimate for a smaller body rather than an official figure. Older children may need nearly as much as an adult. For babies under six months, ask a doctor before using any sunscreen.

How often should I reapply sunscreen when swimming?

The American Academy of Dermatology advises reapplying every two hours and immediately after swimming or sweating. Water-resistant products state on the label whether they last 40 or 80 minutes in the water. The calculator adds a coat after every swim.