A former tour operator says maths can reveal the best places to top up your tan. Kathy Marks reports, while The Independent's travel editor Simon Calder presents a less scientific selection

How to rate the perfect beach? Is it the softness of the sand, the lack of crowds, or the smile of the waiter bringing your pina colada that sets one beach apart from thousands of others?

After carefully considering this most taxing of questions, a German tour operator turned author, Wim de Ruiter, has come up with a mathematical formula that he believes will resolve it once and for all. So for those considering flying off to the sun to escape winter, it might be worth applying his equation before deciding on a destination.

Using this formula (above), Mr de Ruiter has pinpointed the areas containing the world's best 10 beaches. Top ranking goes to the Andaman Islands in the Indian Ocean, followed by the Laccadive Islands, the Maldives and the Seychelles, all in the Indian Ocean. In the south Pacific, Mr de Ruiter names Micronesia, the Marquesas Islands, the Tuamotu Archipelago and Fiji. Finally, in his league table, come the Bahamas and Mexico's Yucatan coast, both in the Caribbean.

The quest for a perfect beach has been an obsession for Mr de Ruiter. The travel brochures, he says, claim the beaches they are promoting have " the finest white sand, with crystal-clear emerald waters". But often holidaymakers are disappointed. So, as unromantic as it seems, Mr de Ruiter has applied hard science to the issue.

"I have closely researched the relevant and objective measurable factors which define the quality of a beach," he says. So, no more airy-fairy statements about swaying palm trees or shimmering seas. Mr de Ruiter's top 10 is based solely on verifiable factors such as sand quality, depth of water and the angle of the sun - which are rated on a scale of 1 to 5.

Less hard-headed observers, he notes, may be affected by "other influences such as clear horizons, cleanliness, crowdedness, ugly buildings, noise, and presence or absence of attractive members of the opposite sex".

None of that for Mr de Ruiter, who spent three decades in the international tourism management business. Explaining how he devised the formula, he says: "White sand is only made by the erosion of coral reefs. Coral can only be found in waters where the temperature never drops below 21C.

"This is why the best beaches are only to be found in the tropics, between 27 degrees north and 27 degrees south of the Equator." And, says Mr de Ruiter, only white sand produces the light-reflecting effect that most holidaymakers crave. He calls this "total reflection".

White sand also feels better. "If you walk with bare feet, you will feel that it is walkable. Darker sands do not reflect light and heat, so you will see people running quickly across it. World-class sands keep cool in the sunshine, while inferior sands become hot."

And geologically older sand is better than new, says Mr de Ruiter, because the older sand features heavily eroded and rounded grains that better reflect the sun.

Now on to those clear turquoise waters. Mr de Ruiter's research has taught him that the sandy bed of the ocean has to be "shallow, with a gentle gradient, to give the best reflection and luminosity".

It all sounds rather dry, and it is difficult to imagine beach quality and sand quality finding their way into travel magazines. But Mr de Ruiter is happy. He describes his labours as "an astonishing and thrilling experience", and he is convinced the perfect beach is only a formula away.

Others may quibble with his top 10 destinations, but there is no question that the Andamans and Laccadives are heavenly spots, which have earned the reputation of tropical paradise.

... OR YOU COULD JUST ASK SIMON CALDER

Best City Beach

Bondi, Sydney, Australia. Bondi offers great urban surfing and good swimming in a beautiful bay fringed with great bars and restaurants.

Best For Children

San Sebastian, Spain. San Sebastian has a dream location, perched on a bay that takes the shape of a shell. The headlands subdue the seas; the sand shelves gently and there is a large, free play area a few yards from the beach.

Best for backpackers

Dominical, Costa Rica. Mainstream tourism has not yet discovered Costa Rica, which means you can still order banana pancakes and listen to Jimi Hendrix at beachside shacks, and stay in \$5-a-night hostels.

Best for comedy

Bedahei, China. As the closest decent resort to Beijing, Bedahei gets very crowded. So there are wardens to make sure everyone behaves, and operate complaints booths for discontented sun-seekers.

Best for inspiration

Luskentyre, Harris, Scotland. The rewards are as immense as the view: which comprises water of implausible clarity, rippling against perfect sand beneath a sky that changes with every moment.

Best for indulgence

Flic en Flac, Mauritius. After a 12-hour overnight flight you need some indulgence, such as that offered by the Taj Exotica Resort and Spa, where your private villa has its own pool, not to mention a garden shower and butler service.

Best for surfing

Fistral, Newquay, Cornwall. The breakers have had over 2,000 miles of Atlantic Ocean to build up energy, which they dissipate in spectacular fashion here.

Best for culture

Zeebrugge, Belgium. For a few weeks each summer, the sand is transformed into anything from cathedrals to comic strip characters, in this art exhibition.

Best for socialism

Varadero, Cuba. Fidel Castro's political dream is kept alive thanks to the earnings from tourist resorts such as this beautiful spit of sand washed by the Atlantic.

Best for skiing

Dubai, United Arab Emirates. Ski Dubai is the biggest indoor ski area in the world. You can swap sunbathing for sub-zero temperatures in minutes.